i have a capri 26 with an universal m2-12 engine. cruising speed is supposed to be between 2700 to 3300 rpm. when i get around 2900 rpm. the boat begins to shake and i can 't go any faster . hull speed is supposed to be 6.4 kn. and i can hardly get to 5.7. Could it be the prop or the shaft alignment. how to know which is wrong . Since the boat is still in the water i can' t any detail on my prop specs. at lower speed ( 2500 rpm ) and lower it works fine
Boat Shaking At High Speed
- Thread starter MORNING LIGHT
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I agree with CCHer - sounds like barnacles or marine growth are fouling your prop. Having a diver go down & clean her at the beginning of the season can help. I'm kinda surprised that a Capri 26 even has an inboard engine. I thought the Capri line was supposed to be more sporty / race oriented and somewhat stripped down. An outboard would've pushed that size boat just fine, and would have no additional drag with the prop lifted on an outboard bracket. My 2 c.
This shaking could be from a few different problems.
1. Bad cutlass bearing
2. Bent prop and or shaft
3. Barnacles on prop and or shaft
4. Bad alignment between couplings (shaft & tranny)
Start with the easiest solution,clean prop and shaft. Check for a bent prop and so on. I've owned s small diesel of that size and never would I run it at rpm's over 2500. You might never see hull speed on any boats by engine alone. Also the speed difference between 2500 rpm's and 3300 will be minimal and fuel consumption will increase significantly. I've heard those are wonderful boats.we had a fleet of Capri 20's that they taught sailing on and they sailed great. Good luck
1. Bad cutlass bearing
2. Bent prop and or shaft
3. Barnacles on prop and or shaft
4. Bad alignment between couplings (shaft & tranny)
Start with the easiest solution,clean prop and shaft. Check for a bent prop and so on. I've owned s small diesel of that size and never would I run it at rpm's over 2500. You might never see hull speed on any boats by engine alone. Also the speed difference between 2500 rpm's and 3300 will be minimal and fuel consumption will increase significantly. I've heard those are wonderful boats.we had a fleet of Capri 20's that they taught sailing on and they sailed great. Good luck
Since i'm in clear water i don't have this problem, i ' ve been told to run the engine at 3300 rpm on neutral to see if it could be a engine problem and no shaking appeared . now my boat is out of the water an the prop seems to be right . i guess it has to be somethig in the shaft alignment . what do you think?
[if i have been trying to run it at 3300 rpm it's because in the universal manual , it says cruising speed is between 2700 and 3300 rpm. i thought i was supposed to reach hull speed with the engine . other wise you are right , this my first boat and i love it.
My Universal manual shows the M-12 with a max rpm of 3600 rpm in neutral. 80% of that would be 2,880 cruising rpm, so you are not far off with no shaking below 2,900 rpm.
I had a bayliner, and hit a rock with the prop, and was still able to run that boat normaly, until i took it out of the water at the end of summer, and their was a huge bend on one of the propellor blades. The boat wasnt as fast after i hit the rock but it didnt act unusuall, it was just slower. I would be inclined to think you have a bent prop shaft, or a missing blade, or something that serious, because when i got that boat out, i couldnt believe it had ran ok with the state of the blades. But even bent, they were the same weight, so it wouldnt make that much difference. If you had three blades, all balancing each other, (and they were three heavy blades, and you lost one) that could cause the problem.
universal engine manual is saying , cruising speed between 2700 to 3300 rpm. i thought i would be able to reach 3000 without shaking. i'm gonna have my prop checked. change the cutlass bearing and i've been told that the pitch on my prop might have something to do with it . next season , we are planning to go in the thousands islands and to get there , it' s 3 1/2 days of motoring against 2 to 3 knots of current. i'd like my boat to sharp and ready to follow the fleet .
thanks for the advices
thanks for the advices
Boat shaking
Your hypothetical hull speed for a 22.9ft LWL is about 6.4Kt...
That would be for light displacement. With water and fuel tanks full, all the cruising apparatus on board etc, what would be your displacement? Your 12hp engine will develop a little less at the prop say 10.5 to 11hp... If you are above 6,000# look at the charts, I don't think you'll get much better than the 5.7 you are getting now.
Also, check your knotmeter, many are off by enormous margins. A two blade prop will vibrate a lot more than a three blade. The three blade will transmit more power.
There might be something wrong with your boat; then again maybe not.
Pierre
Your hypothetical hull speed for a 22.9ft LWL is about 6.4Kt...
That would be for light displacement. With water and fuel tanks full, all the cruising apparatus on board etc, what would be your displacement? Your 12hp engine will develop a little less at the prop say 10.5 to 11hp... If you are above 6,000# look at the charts, I don't think you'll get much better than the 5.7 you are getting now.
Also, check your knotmeter, many are off by enormous margins. A two blade prop will vibrate a lot more than a three blade. The three blade will transmit more power.
There might be something wrong with your boat; then again maybe not.
Pierre
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