|
| Author |
Message |
    
Bruce
| | Posted on Thursday, April 11, 2002 - 09:48 pm: | 
|
Any help on sizing a propeller welcome.
Hull is displacement;15 1/2 feet long; 43in.beam ; round chine lapstreak ; 3HP Copper top Waterman power.Displaces ~ 800# with crew of two. Currently running a 10 x 15 two blade prop.
Prop diameter isn't an issue as prop trails the transom. It vibrates now(Cavitation??)drive line appears tight-no slop. 3/4" shaft.Would three blade help? What diameter and pitch???? |
kevin
| | Posted on Friday, April 12, 2002 - 12:02 am: |
|
Hi Bruce,
Every thing I've read tells me the prop should be in front of the Transom.
Hope this is of help
Kevin |
ernie
| | Posted on Friday, April 12, 2002 - 08:35 am: |
|
Bruce,
I have found that if the prop is not big enough these old engines will run to fast and vibrate. I had a 1.5 hp Caile in a 12 foot boat and had the same problem as you untill I got a big enough prop to hold the rpm down. The rule of thumb is 2 blade square (dia and pitch the same) with the same dia as the flywheel. 3 blade square using the id of the flywheel rim. However on the little Caile I had I had to go even bigger to keep the rpm down. I think I had the prop 3in bigger than the flywheel. I really do not think you have a cavitation problem. Your boat sounds neat. Do you have any pics? I am sure we all would like to see some. Information for posting pics is in the formatting section under documentation on the left of your screen. If you have a problem posting pics you can forward them to myself or to Andrew for posting.
Thanks and hope this helps
Ernie |
miro
| | Posted on Friday, April 12, 2002 - 06:26 pm: |
|
Last summer one of the boats I know had a similar vibration problem and was experiencng cavitation. There is a sort of tinkling bubbling sound that you get when a slow speed prop experiences cavitation. The fix was to mount the prop backwards. This helped quite a bit.
Is there a deadwood in front of the prop? If there is , a 3 blade will help especialy since it is a slow speed prop.
Blade pitch needs to be about as close to synmmetric as you can get. There a number of ways to measure the pitch and many folks have been surprised how different the blades are. I thin Weson Farmer's book descibes a technique. The blades can be tuned to be identical pitch. If you take them to a prop shop get one of the old guys to do it.
miro |
BRUCE
| | Posted on Monday, April 15, 2002 - 08:26 pm: |
|
ERNIE and MIRO- THANKS MUCH FOR THE HELP!!!!!!
BRUCE |
|
|
|
|
