Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 24-04-2008, 23:34   #1
Registered User
 
poundsterling's Avatar

Join Date: Dec 2007
Location: Brisbane, Australia
Boat: Boden, "Helenia" design, 36' Sloop, "Myuna 11'"
Posts: 13
Images: 2
Smile What is the right size propeller.

i have a sloop 36' LOA 32' W/Line 10' Beam 6' Draft, the dead weight when recently lifted from the water was 12 Ton, with full fuel tanks.

She currently has a 17" diameter 2 1/2"pitch fixed prop, driven by a 55HP
Kubota Diesel, but there is plenty of room too accept a larger prop.
I have taken some external measurements and feel she could comfortably
take a 21" diameter 3 1/2"pitched pitched prop.

My question is, is there any set of tables to which one could refer too to see
if it would be worth while increasing the prop size and what would be the likely benefit from increase speed under power?

Cheers, and smooth sailing.
__________________

__________________
Poundsterling

"Some march to the beat of a different drum"
poundsterling is offline   Reply With Quote
Old 25-04-2008, 02:10   #2
Moderator
 
Boracay's Avatar

Cruisers Forum Supporter

Join Date: Feb 2004
Location: Pelican Bay, Great Sandy National Park
Boat: Steel Roberts Offshore 44
Posts: 5,175
Images: 18
Why?

Before you start thinking about new propellers you need to work out how good your present one is.

Q1. What engine speed can you reach with your current propeller (gearbox engaged) with the boat moving at it's maximum speed? Is this above or below the rated max. RPM for your engine.

Q2. What is the maximum speed in knots that you can reach under calm conditions?

Q3. The pitch that you mention looks wrong. Can you check?

Q4. What is your manufacturers specified maximum RPM? What is your gearbox ratio?

Q5. How clean is the propeller/boat below the waterline?

Q6. What diameter exhaust do you have? How high does it lift from the muffler to it's highest point?
__________________

__________________
Rust never sleeps
Boracay Blog.
Boracay is offline   Reply With Quote
Old 26-04-2008, 22:26   #3
Registered User
 
Latitude9.5's Avatar

Join Date: Jun 2006
Boat: CAL 3-46
Posts: 441
Send a message via AIM to Latitude9.5
You can also email michigan wheel with all your info and they will size your prop for you for free.

Michigan Wheel Corporation

They got back to me within 24 hours.
__________________
Latitude9.5 is offline   Reply With Quote
Old 26-04-2008, 22:34   #4
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
There are lots of tables and formulas that can give you a close idea, but ultimately, if a healthy engine cannot reach it maximum rated RPM with a clean hull then the pitch/diameter/number of blades or any combination thereof, is too great.

There are some that subscribe to using a larger propeller saying it is more efficient. BS, diesels are most efficient at higher RPM's. If the diesel cannot reach its maximum rated horsepower then you are effectively lugging the engine and it will not be long before it is prematurely worn out. Also, not one manufacturer is going to tell you that an oversized propeller is a good thing. It is better to be a little undersized than oversized, if anything.

A Google search can bring up formulas for getting you a good idea about the approximate size that will work.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 27-04-2008, 04:52   #5
Registered User

Join Date: Nov 2006
Posts: 976
Images: 6
Hi Poundsterling have sent you a PM....
__________________
cooper is offline   Reply With Quote
Old 28-04-2008, 13:37   #6
Registered User
 
çemberci's Avatar

Join Date: Apr 2008
Location: istanbul/turkey
Posts: 18
size

Quote:
Originally Posted by poundsterling View Post
i have a sloop 36' LOA 32' W/Line 10' Beam 6' Draft, the dead weight when recently lifted from the water was 12 Ton, with full fuel tanks.

She currently has a 17" diameter 2 1/2"pitch fixed prop, driven by a 55HP
Kubota Diesel, but there is plenty of room too accept a larger prop.
I have taken some external measurements and feel she could comfortably
take a 21" diameter 3 1/2"pitched pitched prop.

My question is, is there any set of tables to which one could refer too to see
if it would be worth while increasing the prop size and what would be the likely benefit from increase speed under power?

Cheers, and smooth sailing.
Sir
Please give me the details of your vesells and Engine
Lwl = waterline
Bwl = beam waterline
Draft
* Engine Kubota
Label
engine horsepower
engine rpm
Transmission Ratio
oktay çemberci
__________________
çemberci is offline   Reply With Quote
Old 01-05-2008, 06:30   #7
Registered User
 
poundsterling's Avatar

Join Date: Dec 2007
Location: Brisbane, Australia
Boat: Boden, "Helenia" design, 36' Sloop, "Myuna 11'"
Posts: 13
Images: 2
Thumbs up What is he right size propeller

Thanks to all who took time to reply to my question re the correct size of propeller, sorry for the time it has taken me to respond, but i have been having difficulty logging in, again thanks for the interest
__________________
Poundsterling

"Some march to the beat of a different drum"
poundsterling is offline   Reply With Quote
Old 01-05-2008, 11:22   #8
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Pound,
Hows it coming along?

David
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 01-05-2008, 13:37   #9
Senior Cruiser
 
SkiprJohn's Avatar

Cruisers Forum Supporter

Join Date: May 2006
Location: Kea'au, Big Island, Hawaii
Boat: Cascade, Sloop, 42 - "Casual"
Posts: 14,192
www.cruisersforum.com/forums/f114/proper-prop-size-5972.html

You might try thise one.

Regards,

JohnL
__________________
SkiprJohn is offline   Reply With Quote
Old 17-05-2008, 00:34   #10
Registered User
 
poundsterling's Avatar

Join Date: Dec 2007
Location: Brisbane, Australia
Boat: Boden, "Helenia" design, 36' Sloop, "Myuna 11'"
Posts: 13
Images: 2
Quote:
Originally Posted by David M View Post
Pound,
Hows it coming along?

David
Good day David,

Well the boat is coming along slowly but surely, I am currently preparing to cut out a
section of the hull which has been affect by battery acid spill and replace same.
But having the boat out of the water and looking at the propeller in relation to the size of the hull it seemed a bit small for the job, any from the info sent by fellow members
and suggested sources of information it appears that the current prop should do the job quite adequately

Thanks for your interest.

poundsterling
__________________

__________________
Poundsterling

"Some march to the beat of a different drum"
poundsterling is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Feathering Propeller Ex-Calif Propellers & Drive Systems 17 21-07-2007 16:28
new propeller keller Propellers & Drive Systems 2 22-06-2007 14:14
Propeller generator Stevek Electrical: Batteries, Generators & Solar 14 22-09-2006 10:35
brass propeller irwinsailor Construction, Maintenance & Refit 22 26-01-2006 16:04



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 04:00.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.