Home | Classifieds | History | Technical | Links | Store | About Us | Email
Topics Topics Edit Profile Profile Help/Instructions Help Member List Register  
Search Last 1|3|7 Days Search Search Tree View Tree View  

Propeller sizing

Old Marine Engine » Boats with Early Inboards » Propeller sizing « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

Bruce
Posted on Thursday, April 11, 2002 - 09:48 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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????
Top of pagePrevious messageNext messageBottom of page Link to this message

kevin
Posted on Friday, April 12, 2002 - 12:02 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Hi Bruce,
Every thing I've read tells me the prop should be in front of the Transom.
Hope this is of help
Kevin
Top of pagePrevious messageNext messageBottom of page Link to this message

ernie
Posted on Friday, April 12, 2002 - 08:35 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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
Top of pagePrevious messageNext messageBottom of page Link to this message

miro
Posted on Friday, April 12, 2002 - 06:26 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

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
Top of pagePrevious messageNext messageBottom of page Link to this message

BRUCE
Posted on Monday, April 15, 2002 - 08:26 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

ERNIE and MIRO- THANKS MUCH FOR THE HELP!!!!!!
BRUCE

Add Your Message Here
Post:
Bold text Italics Underline Create a hyperlink Insert a clipart image

Username: Posting Information:
This is a public posting area. Enter your username and password if you have an account. Otherwise, enter your full name as your username and leave the password blank. Your e-mail address is optional.
Password:
E-mail:
Options: Automatically activate URLs in message
Action:

Administration Administration Log Out Log Out   Previous Page Previous Page Next Page Next Page

Home | Classifieds | History | Technical | Links | Store | About Us | Email
&copy 2005 OldMarineEngine.com, P.O. Box 188, Forest Dale, VT 05745-0188 • Phone: 802-247-4864 • All rights reserved.
   Marine Engine Seloc Repair Manual Lookup Tool

marine gas engine repair and restoration