I have a very loud vibration under very low RPM with gear case in forward on my 85 Hunter 34. At higher rpms vibration goes away and do not have it in reverse. Diesel tech believes its cutlass or prop problem. Alignment is OK. Engine is 3GM Yanmar and not sure what existing two blade prop is. What size prop should be on boat for 2 or 3 bladed prop. I am thinking of going to a 3 blade prop for cruising?
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Andy Howard
Low RPM Vibrations
Your onsite mechanic is probably right, but... I've seen several threads on this site about 3GM's and vibration at lower rpm's, my H34 rattles a bit in gear around 800 rpm and that's with a fairly new cutlass bearing and a 3 blade campell prop. However I would not describe what my boat does at lower RPM's as a "very loud vibration". Years ago in an earlier boat I cranked her up one morning and all hell broke loose, I thought she was going to shake apart. It turned out to be a small colony of barnacles making their home on only one propeller blade. So a quick dip in the water is worth doing. If the boat is fairly new to you, go back to your surveyor for suggestions and input. My biggest question would be, "Is this something that I can address at my next haulout or does it need immediate attention?" Yanmar recommends a 15x15 two blade, but hunter used 15x12's on alot of the earlier models, my 1984 included. But that shouldn't be a problem unless your fighting a strong headwind or current. Let us know how this turns out.
Your onsite mechanic is probably right, but... I've seen several threads on this site about 3GM's and vibration at lower rpm's, my H34 rattles a bit in gear around 800 rpm and that's with a fairly new cutlass bearing and a 3 blade campell prop. However I would not describe what my boat does at lower RPM's as a "very loud vibration". Years ago in an earlier boat I cranked her up one morning and all hell broke loose, I thought she was going to shake apart. It turned out to be a small colony of barnacles making their home on only one propeller blade. So a quick dip in the water is worth doing. If the boat is fairly new to you, go back to your surveyor for suggestions and input. My biggest question would be, "Is this something that I can address at my next haulout or does it need immediate attention?" Yanmar recommends a 15x15 two blade, but hunter used 15x12's on alot of the earlier models, my 1984 included. But that shouldn't be a problem unless your fighting a strong headwind or current. Let us know how this turns out.
J
John Miller
More Propeller Information
I am in the process of buying a 1985 Hunter 34. The boat has a propeller that was a 15x15 but it has been reworked to 15x16. It is bent so I am trying to research the correct propeller. The marina said I needed a 15X15 but Marine Diesel Direct shows this to be a 17x11 or 16x13 for two blades and 16x11 for three. The engine is the 3GMF 20 horse with 2.6:1 transmission. Is 15x15 the correct propeller. The engine shakes badly at low RPM but most of that is due to worn motor mounts and the nature of the beast. Most of the engine hoses and belts still have grey paint on them so I am willing to bet the former owners never replaced anything that had not quit working. I guess some people think if it ain't broke, don't fix it. I am replacing all hoses before the boat goes back in the water. As for the vibration, check the mounts, engine alignment and make sure the prop is free of any thing that doesn't belong. It does not take much weight in the wrong place to induce vibration.
I am in the process of buying a 1985 Hunter 34. The boat has a propeller that was a 15x15 but it has been reworked to 15x16. It is bent so I am trying to research the correct propeller. The marina said I needed a 15X15 but Marine Diesel Direct shows this to be a 17x11 or 16x13 for two blades and 16x11 for three. The engine is the 3GMF 20 horse with 2.6:1 transmission. Is 15x15 the correct propeller. The engine shakes badly at low RPM but most of that is due to worn motor mounts and the nature of the beast. Most of the engine hoses and belts still have grey paint on them so I am willing to bet the former owners never replaced anything that had not quit working. I guess some people think if it ain't broke, don't fix it. I am replacing all hoses before the boat goes back in the water. As for the vibration, check the mounts, engine alignment and make sure the prop is free of any thing that doesn't belong. It does not take much weight in the wrong place to induce vibration.
No one knows.
John: I doubt if you can get a 16" prop on this boat and still have proper tip clearance. You need to go to a good prop shop and have them size the proper prop for your boat. If the current prop was in good shape and the bottom/prop was clean you can do some detective work yourself. I think that these boats had from 15 x 15 to 15 x 12. Do you know if you want a 2 blade or 3 blade prop?
John: I doubt if you can get a 16" prop on this boat and still have proper tip clearance. You need to go to a good prop shop and have them size the proper prop for your boat. If the current prop was in good shape and the bottom/prop was clean you can do some detective work yourself. I think that these boats had from 15 x 15 to 15 x 12. Do you know if you want a 2 blade or 3 blade prop?
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Guest
2 blade for less drag
I think I will stay with the 2 blade for now. I looked at a three blade feathering prop but I do not want to put that much in the prop right now. Too many other things to get in order, befor the boat can be launched. I got a call back from Hunter and they said the correct prop is 15x15.
I think I will stay with the 2 blade for now. I looked at a three blade feathering prop but I do not want to put that much in the prop right now. Too many other things to get in order, befor the boat can be launched. I got a call back from Hunter and they said the correct prop is 15x15.
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Kevin
Connection point to flywheel
Hello Brent, If alignment was out the vibration would not be isolated to just the low end. If balance of the propeller was problem it to would not be isolated to the low end. I find it hard to believe that the cutlass bearing is problem because it to is rotation sensitive. My opinion is that it is the damper plate. They will make a banging/changing noise (?) at lower end idle when they are being loaded and unloaded. Once the output loads become greater, as Rpm’s increase, the damper stays compressed and the noise goes away. A thought, hope it helps. Kevin
Hello Brent, If alignment was out the vibration would not be isolated to just the low end. If balance of the propeller was problem it to would not be isolated to the low end. I find it hard to believe that the cutlass bearing is problem because it to is rotation sensitive. My opinion is that it is the damper plate. They will make a banging/changing noise (?) at lower end idle when they are being loaded and unloaded. Once the output loads become greater, as Rpm’s increase, the damper stays compressed and the noise goes away. A thought, hope it helps. Kevin
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Jeff Jones
Damper plate resolution Kevin?
If it is the damper plate (front side on Yanmar 3GM, off crankshaft) is this a sign that something is wrong and needs attention or is it just the nature of the beast? Jeff Jones S/V Escapade
If it is the damper plate (front side on Yanmar 3GM, off crankshaft) is this a sign that something is wrong and needs attention or is it just the nature of the beast? Jeff Jones S/V Escapade
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