Useful Articles
7 TECHNICAL ISSUES TO CONSIDER BEFORE BUYING BOATBy Steve ZimmermanReprinted From Passagemaker Magazine Newsletter, October 22, 2022
Searching for the right boat can be a daunting adventure. First and foremost, a boat must meet your needs with respect to accommodations, performance, appearance and price. Assuming you have found a boat that checks those boxes, the hard work of due diligence begins. And if the due diligence is done well, then you won’t find yourself saying later, “I wish I had known that before I bought the boat.” With that goal in mind, let’s look at seven often-overlooked considerations when buying any kind of boat.
1. GELCOAT COLOR MATTERSGelcoat is a thin, pigmented, resin-rich coating on the outside of the boat. Gelcoat has two functions: to keep the water out of the fiberglass laminate, and to make the boat look pretty. The latter function explains the reason for so many hulls in dark colors such as blue, black, red and forest green.These dark colors lead to two issues: fading and heat. All gelcoat gradually fades, becoming porous and chalky. The dark colors are particularly susceptible to fading, and they reveal the deterioration more dramatically. Additionally, sunshine on dark hulls creates excessive heat; in direct sun, a dark blue hull might reach 170 degrees Fahrenheit, while a white hull in the same conditions would be about 50 degrees cooler.That difference affects the interior temperature in southern and tropical climates, and is why buyers need to think about hull color in terms of more than beauty.
2. BLISTERS ARE NOT A DEAL KILLERDiscovering blisters on survey day often prompts buyers to walk away—a mistake, in my view.Blisters certainly need to be addressed, including peeling away the damaged laminates, applying new laminates with vinylester resin, and sealing the result with a barrier coat system. The presence of vinylester matters to a buyer of a new boat, or to the purchaser of a boat that has had blisters repaired, because vinylester resists moisture penetration far better than polyester resin. Keeping the moisture out prevents blisters. The result can be a bottom that is stronger than the original and protected from blisters for 15 years or more.If you can negotiate a reasonable discount into the post-survey purchase price, then don’t let blisters scare you off. And keep in mind that a boat with no blisters might develop them later, depending upon change in location and duration of exposure.Maybe you are buying a Great Lakes boat that has been kept in cold, fresh water and stored on land each winter. After purchase, the boat moves to Florida, where it stays in warm salt water year-round. After a couple of years, blisters might appear, but a boat that had a blister problem and received the full treatment would be unaffected by the changed conditions.
2. CHINE SLAP CAN KEEP YOU UP AT NIGHTBoats with hard chines or low spray rails form a wedge-shaped pocket at the waterline near the bow. At anchor with even a minor chop, the wavelets hit this wedge and make a slap or chunk sound. You not only hear this happen; you often can feel it.If the boat has a master stateroom in the bow, then the slap can be annoying enough to keep you awake at night. If you have never experienced this condition, then you might want to drop the anchor on the day of the survey and spend a little time in the forward stateroom.
3. "CAPTAIN MAINTAINED" SOMETIMES MEANS "BUYER BEWARE"Certainly, a full-time captain with strong technical skills, willing hands and a penchant for detail can keep a boat in outstanding condition. In my experience, however, the words “captain maintained” in a brokerage advertisement often turn out to be a negative.On boats smaller than 70 feet length overall, the captain is rarely a full-time presence on the boat. Many captains run several boats, showing up when an owner wants to make a trip, and checking on each boat from time to time.Many repairs are made on the fly to keep the boat running while the owner stays aboard. Resourcefulness and creativity pay off in those situations, solving an immediate problem and keeping the boat moving. Too often, however, these quick fixes become permanent, forgotten until they are discovered on survey day, in bunches.Additionally, some captains are on a maintenance budget and benefit from keeping costs down—another driver of quick fixes.
5. CORE MATERIAL MATTERSIf you are buying a composite (fiberglass) boat, then you can count on two things: the hull and/or deck will have core material between fiberglass skins, and there will be elevated moisture found somewhere during the survey.A good marine surveyor will provide a context for the moisture readings, and guidance on the structural significance. Except when balsa core is involved, even high readings on a moisture meter rarely have structural implications. Establishing the significance of the findings will depend on three considerations: the severity of the readings, the size and number of the affected areas, and the type of core material.Moisture in the core usually affects value to a greater degree than it affects the strength of the structure. Balsa core provides the exception. If chronically exposed to moisture content on the high range of a meter, balsa core will decompose into something resembling wet cardboard. Once that happens, you are in for extensive, costly repairs. 6. LOW ENGINE HOURS TELL TWO STORIESLow engine hours potentially bode well for engine longevity, provided the boat has been maintained well and run primarily at the rated recreational performance load. Engine brand and model matters; some engines have been designed for relatively low hours between rebuilds (6,000 hours, for example), while others have been engineered for much higher spans (10,000 hours, for example).But exceptionally low engine hours tell another story, one about a boat that has had very light use. During the first few months to a year of ownership with a former “marina queen,” you should be prepared for sporadic failures of system components: head vacuum pump, air conditioning condenser, generator exhaust riser and so on.Previous light use doesn’t mean you shouldn’t buy the boat, but it does mean you will need some time aboard before heading off on a long trip, and some room in the budget.
7. DON'T GET HOSEDCruising boats have a surprising amount of hose. A 40-foot trawler might have 200 or 300 feet or more of fuel, sanitation, engine, hydraulic and seacock hoses. Fuel fill hose costs roughly $20 per foot, while good sanitation hose will come closer to $30 per foot. And replacing hoses can be shockingly time consuming. Just imagine the run of sanitation hose from a tank in the bilge through cabinetry and up to the deck.Most of us don’t replace hoses until they fail, but they do have a service life that varies depending on the hose type and application. While 20-year-old hoses can still be in use, 10 years should be your benchmark, and less than that for hoses on the engine and generator.Replacing all the hoses on a 40-foot trawler might cost $20,000—money well spent, but likely more than you thought about on survey day.
The UpshotAny boat post-purchase will present some surprises and challenges. With careful forethought and an excellent survey, you will minimize those unknowns and be prepared for what the boat will need.Once you have bought the boat, there is one more test that every boat should pass. When you drop the anchor and head out in the dinghy, if you find yourself gazing back at the boat with a good feeling, then you have chosen well.If you make a full circle around the boat to admire it before heading ashore, then you get bonus points.
Steve Zimmerman is the president of Zimmerman Marine, which operates five boatyards in Maryland, Virginia, North Carolina and South Carolina. Zimmerman has been building and repairing boats for more than four decades.
Searching for the right boat can be a daunting adventure. First and foremost, a boat must meet your needs with respect to accommodations, performance, appearance and price. Assuming you have found a boat that checks those boxes, the hard work of due diligence begins. And if the due diligence is done well, then you won’t find yourself saying later, “I wish I had known that before I bought the boat.” With that goal in mind, let’s look at seven often-overlooked considerations when buying any kind of boat.
1. GELCOAT COLOR MATTERSGelcoat is a thin, pigmented, resin-rich coating on the outside of the boat. Gelcoat has two functions: to keep the water out of the fiberglass laminate, and to make the boat look pretty. The latter function explains the reason for so many hulls in dark colors such as blue, black, red and forest green.These dark colors lead to two issues: fading and heat. All gelcoat gradually fades, becoming porous and chalky. The dark colors are particularly susceptible to fading, and they reveal the deterioration more dramatically. Additionally, sunshine on dark hulls creates excessive heat; in direct sun, a dark blue hull might reach 170 degrees Fahrenheit, while a white hull in the same conditions would be about 50 degrees cooler.That difference affects the interior temperature in southern and tropical climates, and is why buyers need to think about hull color in terms of more than beauty.
2. BLISTERS ARE NOT A DEAL KILLERDiscovering blisters on survey day often prompts buyers to walk away—a mistake, in my view.Blisters certainly need to be addressed, including peeling away the damaged laminates, applying new laminates with vinylester resin, and sealing the result with a barrier coat system. The presence of vinylester matters to a buyer of a new boat, or to the purchaser of a boat that has had blisters repaired, because vinylester resists moisture penetration far better than polyester resin. Keeping the moisture out prevents blisters. The result can be a bottom that is stronger than the original and protected from blisters for 15 years or more.If you can negotiate a reasonable discount into the post-survey purchase price, then don’t let blisters scare you off. And keep in mind that a boat with no blisters might develop them later, depending upon change in location and duration of exposure.Maybe you are buying a Great Lakes boat that has been kept in cold, fresh water and stored on land each winter. After purchase, the boat moves to Florida, where it stays in warm salt water year-round. After a couple of years, blisters might appear, but a boat that had a blister problem and received the full treatment would be unaffected by the changed conditions.
2. CHINE SLAP CAN KEEP YOU UP AT NIGHTBoats with hard chines or low spray rails form a wedge-shaped pocket at the waterline near the bow. At anchor with even a minor chop, the wavelets hit this wedge and make a slap or chunk sound. You not only hear this happen; you often can feel it.If the boat has a master stateroom in the bow, then the slap can be annoying enough to keep you awake at night. If you have never experienced this condition, then you might want to drop the anchor on the day of the survey and spend a little time in the forward stateroom.
3. "CAPTAIN MAINTAINED" SOMETIMES MEANS "BUYER BEWARE"Certainly, a full-time captain with strong technical skills, willing hands and a penchant for detail can keep a boat in outstanding condition. In my experience, however, the words “captain maintained” in a brokerage advertisement often turn out to be a negative.On boats smaller than 70 feet length overall, the captain is rarely a full-time presence on the boat. Many captains run several boats, showing up when an owner wants to make a trip, and checking on each boat from time to time.Many repairs are made on the fly to keep the boat running while the owner stays aboard. Resourcefulness and creativity pay off in those situations, solving an immediate problem and keeping the boat moving. Too often, however, these quick fixes become permanent, forgotten until they are discovered on survey day, in bunches.Additionally, some captains are on a maintenance budget and benefit from keeping costs down—another driver of quick fixes.
5. CORE MATERIAL MATTERSIf you are buying a composite (fiberglass) boat, then you can count on two things: the hull and/or deck will have core material between fiberglass skins, and there will be elevated moisture found somewhere during the survey.A good marine surveyor will provide a context for the moisture readings, and guidance on the structural significance. Except when balsa core is involved, even high readings on a moisture meter rarely have structural implications. Establishing the significance of the findings will depend on three considerations: the severity of the readings, the size and number of the affected areas, and the type of core material.Moisture in the core usually affects value to a greater degree than it affects the strength of the structure. Balsa core provides the exception. If chronically exposed to moisture content on the high range of a meter, balsa core will decompose into something resembling wet cardboard. Once that happens, you are in for extensive, costly repairs. 6. LOW ENGINE HOURS TELL TWO STORIESLow engine hours potentially bode well for engine longevity, provided the boat has been maintained well and run primarily at the rated recreational performance load. Engine brand and model matters; some engines have been designed for relatively low hours between rebuilds (6,000 hours, for example), while others have been engineered for much higher spans (10,000 hours, for example).But exceptionally low engine hours tell another story, one about a boat that has had very light use. During the first few months to a year of ownership with a former “marina queen,” you should be prepared for sporadic failures of system components: head vacuum pump, air conditioning condenser, generator exhaust riser and so on.Previous light use doesn’t mean you shouldn’t buy the boat, but it does mean you will need some time aboard before heading off on a long trip, and some room in the budget.
7. DON'T GET HOSEDCruising boats have a surprising amount of hose. A 40-foot trawler might have 200 or 300 feet or more of fuel, sanitation, engine, hydraulic and seacock hoses. Fuel fill hose costs roughly $20 per foot, while good sanitation hose will come closer to $30 per foot. And replacing hoses can be shockingly time consuming. Just imagine the run of sanitation hose from a tank in the bilge through cabinetry and up to the deck.Most of us don’t replace hoses until they fail, but they do have a service life that varies depending on the hose type and application. While 20-year-old hoses can still be in use, 10 years should be your benchmark, and less than that for hoses on the engine and generator.Replacing all the hoses on a 40-foot trawler might cost $20,000—money well spent, but likely more than you thought about on survey day.
The UpshotAny boat post-purchase will present some surprises and challenges. With careful forethought and an excellent survey, you will minimize those unknowns and be prepared for what the boat will need.Once you have bought the boat, there is one more test that every boat should pass. When you drop the anchor and head out in the dinghy, if you find yourself gazing back at the boat with a good feeling, then you have chosen well.If you make a full circle around the boat to admire it before heading ashore, then you get bonus points.
Steve Zimmerman is the president of Zimmerman Marine, which operates five boatyards in Maryland, Virginia, North Carolina and South Carolina. Zimmerman has been building and repairing boats for more than four decades.
Reprinted from:POWER & MOTORYACHTJanuary 31, 2022
A Case of the ShakesSteve Zimmerman & Max Parker
Being out on the water presents a wonderful opportunity to de-stress, but too much vibration can shake your hardware loose and detract from your enjoyment.A recent pre-purchase survey excessive vibration and recommended a repair. After the purchase, the buyers took the boat to a repair yard, where the shaft was replaced. Unfortunately, the problem persisted, and they visited another repair facility that suspected the prop and removed it for reconditioning.As you might have guessed, after the work at both yards, the problem remained. The owners’ story is a lesson in how challenging it can be to diagnose vibration problems correctly.First Things FirstStart by having a mechanic come on board for a test run as a technician with trained eyes and ears can uncover problems that an owner may not recognize.There was no question something was up. Starting around 2500 rpm, a thrumming sound radiated from the drivetrain. This disturbance only increased the faster the boat went.The boat may need to be hauled to verify the propeller condition. In addition to marine growth, the remains of a crab-pot line can also give a boat the shakes.PropellersThe hunt begins with an inspection of the prop before messing with the drivetrain. The most conclusive diagnosis involves removing the prop and sending it out for a digital scan. You can check for any gross variations without removing the prop. Using vise grips or a similar tool, clamp a metal rod to the rudder and adjust it so that the end barely grazes the edge of the propeller at its widest point. Then, rotate the prop to the next blade and compare the clearance. It should not vary by more than one-sixteenth of an inch. Repeat this process for each blade, and then move the rod out closer to the blade tips and repeat.To check for bent prop blades prior to a trip to the prop shop, clamp a rod to the rudder that just touches one blade. Spin the prop and watch the rod for any difference between blades.There can be issues with two-legged struts and four-bladed props. Since two of the prop blades can be shielded on each rotation, a noticeable vibration can occur. You should have a space of at least 15 percent of the prop diameter between the prop’s tips and the hull. Less space than that, and the prop will make noise as it passes the hull.If the vibration is new, these causes are not in play. If the vibration developed after removal of the propeller, then the prop might not be properly installed. In the case of our example, the prop had just been reconditioned and fitted properly on the taper, so further investigation was required.The ShaftFirst, the shaft might be bent. A bent shaft can often be detected while it’s still installed in the boat. Check it with a caliper while slowly rotating the shaft. The bend, however, might be at an inaccessible portion of the shaft, requiring removal for inspection. Prop shaft couplings transfer all the engine’s thrust to the propeller shaft. They must be precisely machined to fit each shaft.The second way the shaft can cause vibration is through lack of adequate support. There are well-established protocols for the bearing support for each diameter of shaft. Lack of adequate support can lead to shaft “whipping.”There may be too much shaft to overhang the after cutlass bearing (only 1½ times the shaft diameter is allowed between the forward end of the prop and the closest support). Or, the cutlass bearings may simply be worn out.Engine MountsMotor mounts are basically two metal plates with rubber between them. Worn or damaged mounts can transfer too much vibration to the boat. If you’re lucky, the motor mounts are in good shape, not rusty or older than the manufacturer’s recommendation for replacement. Mounts often get neglected, sometimes to the point of the rubber becoming completely disconnected from the metal.The motor mount under the raw-water pump is often the worst of the bunch. Raw-water pumps have a weep hole in the housing near the pump’s shaft. The weep hole shows any leaks: green indicates a seawater leak, while oil residue indicates a failing oil seal. A leaking raw-water pump will slowly but surely destroy the engine mount beneath it.Motor mounts should be checked before a trial run to be sure that all the fasteners are tight. Another check should be done underway and under load while shifting the boat in and out of gear to be sure there is not too much movement. You shouldn’t see them flex more than about an eighth of an inch.AlignmentThe shaft must align to the engine within very tight tolerances. A collar (referred to as the “coupling”) fits on the forward end of the shaft and bolts to a flange on the transmission. A coupling is a precisely machined steel component that transfers the rotational energy of the transmission to the shaft.The American Boat and Yacht Council recommends that the face of the transmission coupling and the face of the prop shaft coupling have no more than .004 of an inch in misalignment. Any more than that, and there can be excessive vibration, accelerated cutlass bearing wear and even transmission damage.In some cases, an engine cannot be aligned because the shaft is misaligned with the shaft log or bearings. When that happens, the boat must be hauled, and if there are struts, they may have to be removed and reset. If there aren’t struts, then the shaft log may have to be removed and reset.It is always good, in any case, to check the cutlass bearings and make sure they are not worn or loose. Many boats have cutlass bearings abaft the stuffing box that are not visible until the box and shaft are removed. TransmissionsThere is a device between the engine and transmission that reduces the shock loads of shifting. This device is called a damper plate. It is in the bell housing between the engine and transmission. It utilizes either springs or rubber for mitigation, and once that material wears out or breaks, the damper plate can make an awful racket.Most transmissions run relatively quietly unless there is a gear failure inside. It’s usually easy to pinpoint where the noise is coming from when this happens, and the source is typically going to be evident in gear at low rpm.Vibration CouplingsA variety of additional couplings can be installed between the transmission coupling and the prop shaft. These can be simple, flexible couplings (like a DriveSaver) that mount directly to the transmission between the two metal couplings. Or, they can be a more sophisticated constant velocity joint-type system that utilizes a short jack shaft and a bearing fixed to the hull. The constant velocity joint style allows for softer engine mounts and slight engine misalignment.There is a lifespan to constant velocity joints, and to any rotating component that utilizes rubber or plastic. As these systems wear out, they can cause the vibrations and noises they are meant to suppress.Flexible insert couplings, because their plastic faces are not machined, can’t be used to get a true alignment. This method can’t be used as a final alignment since the boat typically has to be hauled. As solid as your boat feels in the water, the hull will change shape as it is brought onto land and blocked. Wait at least 24 hours after launching for the hull to retain its shape before completing a final alignment.The CulpritOn the boat in our example, the propeller had been serviced, the shaft had been replaced, and both checked out fine. In addition, the alignment fell within the required ABYC standard. Further inspection ruled out any problems with the engine or transmission, and the culprit remained elusive.Let’s return to the coupling on the forward end of the shaft. The coupling can be held to the shaft with a taper, a key and a nut (like a prop), or a straight shaft can be used with a key and set screws through the coupling to the shaft. There are also split couplings that use bolts to squeeze onto the shaft.Having ruled out the other possibilities, we removed the shaft and sent it and the coupling to the machine shop. The machinist found that the coupling face wasn’t perpendicular to the shaft, a problem that induced a wobble and, hence, vibration.The lesson: Whenever a shaft is replaced, the coupling must be sent to the machine shop to make sure they match up.If you have been living with annoying vibration, you will be amazed and delighted when you head out on a boat that hums smoothly. Your boat will be more enjoyable, hardware won’t come loose, and you’ll start feeling those good vibrations.
A Case of the ShakesSteve Zimmerman & Max Parker
Being out on the water presents a wonderful opportunity to de-stress, but too much vibration can shake your hardware loose and detract from your enjoyment.A recent pre-purchase survey excessive vibration and recommended a repair. After the purchase, the buyers took the boat to a repair yard, where the shaft was replaced. Unfortunately, the problem persisted, and they visited another repair facility that suspected the prop and removed it for reconditioning.As you might have guessed, after the work at both yards, the problem remained. The owners’ story is a lesson in how challenging it can be to diagnose vibration problems correctly.First Things FirstStart by having a mechanic come on board for a test run as a technician with trained eyes and ears can uncover problems that an owner may not recognize.There was no question something was up. Starting around 2500 rpm, a thrumming sound radiated from the drivetrain. This disturbance only increased the faster the boat went.The boat may need to be hauled to verify the propeller condition. In addition to marine growth, the remains of a crab-pot line can also give a boat the shakes.PropellersThe hunt begins with an inspection of the prop before messing with the drivetrain. The most conclusive diagnosis involves removing the prop and sending it out for a digital scan. You can check for any gross variations without removing the prop. Using vise grips or a similar tool, clamp a metal rod to the rudder and adjust it so that the end barely grazes the edge of the propeller at its widest point. Then, rotate the prop to the next blade and compare the clearance. It should not vary by more than one-sixteenth of an inch. Repeat this process for each blade, and then move the rod out closer to the blade tips and repeat.To check for bent prop blades prior to a trip to the prop shop, clamp a rod to the rudder that just touches one blade. Spin the prop and watch the rod for any difference between blades.There can be issues with two-legged struts and four-bladed props. Since two of the prop blades can be shielded on each rotation, a noticeable vibration can occur. You should have a space of at least 15 percent of the prop diameter between the prop’s tips and the hull. Less space than that, and the prop will make noise as it passes the hull.If the vibration is new, these causes are not in play. If the vibration developed after removal of the propeller, then the prop might not be properly installed. In the case of our example, the prop had just been reconditioned and fitted properly on the taper, so further investigation was required.The ShaftFirst, the shaft might be bent. A bent shaft can often be detected while it’s still installed in the boat. Check it with a caliper while slowly rotating the shaft. The bend, however, might be at an inaccessible portion of the shaft, requiring removal for inspection. Prop shaft couplings transfer all the engine’s thrust to the propeller shaft. They must be precisely machined to fit each shaft.The second way the shaft can cause vibration is through lack of adequate support. There are well-established protocols for the bearing support for each diameter of shaft. Lack of adequate support can lead to shaft “whipping.”There may be too much shaft to overhang the after cutlass bearing (only 1½ times the shaft diameter is allowed between the forward end of the prop and the closest support). Or, the cutlass bearings may simply be worn out.Engine MountsMotor mounts are basically two metal plates with rubber between them. Worn or damaged mounts can transfer too much vibration to the boat. If you’re lucky, the motor mounts are in good shape, not rusty or older than the manufacturer’s recommendation for replacement. Mounts often get neglected, sometimes to the point of the rubber becoming completely disconnected from the metal.The motor mount under the raw-water pump is often the worst of the bunch. Raw-water pumps have a weep hole in the housing near the pump’s shaft. The weep hole shows any leaks: green indicates a seawater leak, while oil residue indicates a failing oil seal. A leaking raw-water pump will slowly but surely destroy the engine mount beneath it.Motor mounts should be checked before a trial run to be sure that all the fasteners are tight. Another check should be done underway and under load while shifting the boat in and out of gear to be sure there is not too much movement. You shouldn’t see them flex more than about an eighth of an inch.AlignmentThe shaft must align to the engine within very tight tolerances. A collar (referred to as the “coupling”) fits on the forward end of the shaft and bolts to a flange on the transmission. A coupling is a precisely machined steel component that transfers the rotational energy of the transmission to the shaft.The American Boat and Yacht Council recommends that the face of the transmission coupling and the face of the prop shaft coupling have no more than .004 of an inch in misalignment. Any more than that, and there can be excessive vibration, accelerated cutlass bearing wear and even transmission damage.In some cases, an engine cannot be aligned because the shaft is misaligned with the shaft log or bearings. When that happens, the boat must be hauled, and if there are struts, they may have to be removed and reset. If there aren’t struts, then the shaft log may have to be removed and reset.It is always good, in any case, to check the cutlass bearings and make sure they are not worn or loose. Many boats have cutlass bearings abaft the stuffing box that are not visible until the box and shaft are removed. TransmissionsThere is a device between the engine and transmission that reduces the shock loads of shifting. This device is called a damper plate. It is in the bell housing between the engine and transmission. It utilizes either springs or rubber for mitigation, and once that material wears out or breaks, the damper plate can make an awful racket.Most transmissions run relatively quietly unless there is a gear failure inside. It’s usually easy to pinpoint where the noise is coming from when this happens, and the source is typically going to be evident in gear at low rpm.Vibration CouplingsA variety of additional couplings can be installed between the transmission coupling and the prop shaft. These can be simple, flexible couplings (like a DriveSaver) that mount directly to the transmission between the two metal couplings. Or, they can be a more sophisticated constant velocity joint-type system that utilizes a short jack shaft and a bearing fixed to the hull. The constant velocity joint style allows for softer engine mounts and slight engine misalignment.There is a lifespan to constant velocity joints, and to any rotating component that utilizes rubber or plastic. As these systems wear out, they can cause the vibrations and noises they are meant to suppress.Flexible insert couplings, because their plastic faces are not machined, can’t be used to get a true alignment. This method can’t be used as a final alignment since the boat typically has to be hauled. As solid as your boat feels in the water, the hull will change shape as it is brought onto land and blocked. Wait at least 24 hours after launching for the hull to retain its shape before completing a final alignment.The CulpritOn the boat in our example, the propeller had been serviced, the shaft had been replaced, and both checked out fine. In addition, the alignment fell within the required ABYC standard. Further inspection ruled out any problems with the engine or transmission, and the culprit remained elusive.Let’s return to the coupling on the forward end of the shaft. The coupling can be held to the shaft with a taper, a key and a nut (like a prop), or a straight shaft can be used with a key and set screws through the coupling to the shaft. There are also split couplings that use bolts to squeeze onto the shaft.Having ruled out the other possibilities, we removed the shaft and sent it and the coupling to the machine shop. The machinist found that the coupling face wasn’t perpendicular to the shaft, a problem that induced a wobble and, hence, vibration.The lesson: Whenever a shaft is replaced, the coupling must be sent to the machine shop to make sure they match up.If you have been living with annoying vibration, you will be amazed and delighted when you head out on a boat that hums smoothly. Your boat will be more enjoyable, hardware won’t come loose, and you’ll start feeling those good vibrations.
The Crew
.jpg)
Copyright 2022 Puls Marine Surveying, LLC. All rights reserved.