I've had some knocking on my hull since purchasing my boat. The yard has aligned my engine, and raised it to center the shaft. The noise it better, but still there at certain rpms. I'm told that replacing the bronze shaft with a stainless steel shaft will help cut down on the shaft flexing. Has anyone else encountered this?
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terry dornan
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Rick Spear
The cutlass bearing has been checked
The shaft is actually vibrating against the hull. There is a shiney spot on the shaft where it hits.
The shaft is actually vibrating against the hull. There is a shiney spot on the shaft where it hits.
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Bryan C
Gotta be out of alignment or bent
Shaft shouldn't be vibrating. I don't believe they flex, either. Assuming the shaft is properly aligned, if its rubbing against the hull, may be bent. Put in neutral, jump in with a mask (I realize this might be not fun in CT) and hand turn shaft to see if it is true or if it is rotating into the hull where it is hitting. If it is bent, probably need to replace at next haul-out otherwise you may wear out you cutlass bearings.
Shaft shouldn't be vibrating. I don't believe they flex, either. Assuming the shaft is properly aligned, if its rubbing against the hull, may be bent. Put in neutral, jump in with a mask (I realize this might be not fun in CT) and hand turn shaft to see if it is true or if it is rotating into the hull where it is hitting. If it is bent, probably need to replace at next haul-out otherwise you may wear out you cutlass bearings.
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Kevin L. Woody
Knocking
Hello Rick, Thanks for the letter. Even with the shaft in complete alignment and cutlass bearings in good order, the shaft at certain Rpm's may still have the capability of contacting the stern tube. If the shaft is bronze it's flex rate is higher then a 316, Aquamet or equivalent material. This could very easily allow the shaft to whip in an elliptical manner causing stern tube contact. If the cutlass bearing was worn out you would most likely see vibration and knocking at all ranges of Rpm's and not just isolated Rpm's. I would guess that if you could measure the load on the running gear you would find that at the point it begins to knock, the running gear loads are highest. The higher the loads the more likely the shaft will flex in it’s midsection. I had a similar problem on my sailboat and could not figure it out. It was not until I was cleaning the hull underwater that I shook the shaft and duplicated the noise, which allowed me to then determine it was the shaft coming in contact with the stern tube. This forced me to replace the shafting material from 316 to Aquamet 22. No more contact for me. Sincerely, Kevin L. Woody
Hello Rick, Thanks for the letter. Even with the shaft in complete alignment and cutlass bearings in good order, the shaft at certain Rpm's may still have the capability of contacting the stern tube. If the shaft is bronze it's flex rate is higher then a 316, Aquamet or equivalent material. This could very easily allow the shaft to whip in an elliptical manner causing stern tube contact. If the cutlass bearing was worn out you would most likely see vibration and knocking at all ranges of Rpm's and not just isolated Rpm's. I would guess that if you could measure the load on the running gear you would find that at the point it begins to knock, the running gear loads are highest. The higher the loads the more likely the shaft will flex in it’s midsection. I had a similar problem on my sailboat and could not figure it out. It was not until I was cleaning the hull underwater that I shook the shaft and duplicated the noise, which allowed me to then determine it was the shaft coming in contact with the stern tube. This forced me to replace the shafting material from 316 to Aquamet 22. No more contact for me. Sincerely, Kevin L. Woody
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Bryan C.
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Bill Meyer
Rapping at 2400 RPM
I don't have the answer to your problem, but my situation is somewhat similar. I am now looking at possible cavitation. After that, must consider the transmission. Please stay in touch and I will do the same. The following is my saga: Re: Hunter Legend 37 (88) 3HM35F Yanmar Last year the boat developed a groaning (R.R.R.R.) sound or a laboring sound between 1800 2300 RPM. Over 2300 the groaning either subsided or was not noticeable. The alignment was checked (O.K.) but the sound stayed with the boat. From my description, my mechanic felt it related to clutch cones in the transmission. This transmission does not operate with clutch cones. Earlier this season a rattling sound was added when throttle moved with short movements back/forth at under 2000 RPM. I could also create the same rattling sound when putting pressure on the shaft inside the boat. I have taken the following steps to isolate the problem: 1. No noticeable engine vibration 2. No boat vibration when standing at helm 3. Transmission in neutral at 3500 RPM (boat and engine run smooth) 4. Boat in reverse at 2100 RPM no groaning or rattling 5. Checked the propeller (17x10 RH 2 Blade as per specs) 6. Checked the shaft (1" s/s on the lathe - True) 7. Replaced cutlass bearing 8. Replaced Shaft flange and checked shaft lock bolts 9. Removed transmission for visual check test under load 10.Realigned shaft 11.Checked engine mounts All of the above did nothing to resolve the noise problem! Groaning at 2100 RPM + or - and rattling when moving the throttle forward/back. I am ready to take advice. Can anybody help?
I don't have the answer to your problem, but my situation is somewhat similar. I am now looking at possible cavitation. After that, must consider the transmission. Please stay in touch and I will do the same. The following is my saga: Re: Hunter Legend 37 (88) 3HM35F Yanmar Last year the boat developed a groaning (R.R.R.R.) sound or a laboring sound between 1800 2300 RPM. Over 2300 the groaning either subsided or was not noticeable. The alignment was checked (O.K.) but the sound stayed with the boat. From my description, my mechanic felt it related to clutch cones in the transmission. This transmission does not operate with clutch cones. Earlier this season a rattling sound was added when throttle moved with short movements back/forth at under 2000 RPM. I could also create the same rattling sound when putting pressure on the shaft inside the boat. I have taken the following steps to isolate the problem: 1. No noticeable engine vibration 2. No boat vibration when standing at helm 3. Transmission in neutral at 3500 RPM (boat and engine run smooth) 4. Boat in reverse at 2100 RPM no groaning or rattling 5. Checked the propeller (17x10 RH 2 Blade as per specs) 6. Checked the shaft (1" s/s on the lathe - True) 7. Replaced cutlass bearing 8. Replaced Shaft flange and checked shaft lock bolts 9. Removed transmission for visual check test under load 10.Realigned shaft 11.Checked engine mounts All of the above did nothing to resolve the noise problem! Groaning at 2100 RPM + or - and rattling when moving the throttle forward/back. I am ready to take advice. Can anybody help?
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Rick Spear
I'll be changing the shaft in the off season
Thanks Kevin for your answer. It confirms what the people in my yard were suggesting.
Thanks Kevin for your answer. It confirms what the people in my yard were suggesting.
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ted
packing material
i had the same problem, ended up being the packing material in the stuffing box, replaced it and the problem went away.
i had the same problem, ended up being the packing material in the stuffing box, replaced it and the problem went away.
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Patrick Ewing
Same Problem
Our 37.5 had this same knocking problem and we tried all of the usual fixes - alignment etc.. This summer I replaced the 2 blade 17" Max-Prop with a 3 blade 18" Max-Prop and NO MORE PROBLEM. Picked up almost a full knot of speed and there is no more knocking at any speed. I do intend to reinforce the strut with a backing plate inside the hull this spring. I watched it flex when under way and vibrating (with the old prop) and was amazed that it didn't break the hull. You might try adding a backing plate to yours if it looks like it is doing that also.
Our 37.5 had this same knocking problem and we tried all of the usual fixes - alignment etc.. This summer I replaced the 2 blade 17" Max-Prop with a 3 blade 18" Max-Prop and NO MORE PROBLEM. Picked up almost a full knot of speed and there is no more knocking at any speed. I do intend to reinforce the strut with a backing plate inside the hull this spring. I watched it flex when under way and vibrating (with the old prop) and was amazed that it didn't break the hull. You might try adding a backing plate to yours if it looks like it is doing that also.
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Alex
Shaft too long..?
I read an article suggesting such occurence on production boats,if a. unsupported shaft( between cutless bearing and gear ) too long along with new softer engine supports; it flex in the middle, touching the stern tube b. this fault may cause in time the shaft to bend!!. There is data -at shaft/stern gear producers-what is the max lenght for certain shaft diameter and shaft . I would advise to look into it.
I read an article suggesting such occurence on production boats,if a. unsupported shaft( between cutless bearing and gear ) too long along with new softer engine supports; it flex in the middle, touching the stern tube b. this fault may cause in time the shaft to bend!!. There is data -at shaft/stern gear producers-what is the max lenght for certain shaft diameter and shaft . I would advise to look into it.
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Bill Meyer
3 Blade Max Prop - Question
Re: Hunter 37 Rapping - Thank you for your timely reply, Patrick. My next move is to try a 3 Blade Prop. I have 3 inches between the present 17" Diam. Prop and the hull. Recommended space is 15% so an 18" Diam. 3 Blade Prop would just make it. My question, Patrick, is why did you go to an 18" Diam. and what pitch do you have on the replacement prop? Also what motor do you have? Thanks for your help. Bill
Re: Hunter 37 Rapping - Thank you for your timely reply, Patrick. My next move is to try a 3 Blade Prop. I have 3 inches between the present 17" Diam. Prop and the hull. Recommended space is 15% so an 18" Diam. 3 Blade Prop would just make it. My question, Patrick, is why did you go to an 18" Diam. and what pitch do you have on the replacement prop? Also what motor do you have? Thanks for your help. Bill
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