SailNet Community - Reply to Topic
Thread: Prop size? Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

  Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below

  Topic Review (Newest First)
05-29-2007 05:52 PM
JimsCAL I agree with getting recommendations from a prop manufacturer. Keep ijn mind that going to a smaller diameter prop but leaving the pitch the same will basically increase slip. The RPMs may go up, but you are not getting more thust to move the boat - inefficient!. Reducing the pitch will increase the engine RPM at a particular boat speed which sounds like what you want. I am however surprised a 10 inch pitch doesn't work for you as the prop RPM is pretty low with the 2.62 gear ratio you report.
05-29-2007 11:36 AM
Gary M Select a prop manufacturer and give them these details and ask them. They will also need the distance from centre of shaft to bottom of hull.
They are usually very quick with a reply and certainly are familiar with the Cat 27s.

05-29-2007 11:17 AM
Originally Posted by Hawkeye25
Just my two cents, I think the 12x10 should be fine and your cruise RPM @ 5.5 kts should be around 2800 . . .
Thanks for the information. I think it is consistent with what my mechanic is saying.

A couple of points, just for clarity, though. She's got a 14-10 right now and can't make 2,800 rpm. I can only get to about 2,500 rpm.
05-29-2007 11:14 AM
Hawkeye25 Just my two cents, I think the 12x10 should be fine and your cruise RPM @ 5.5 kts should be around 2800, with the engine capable of reaching 3600 if it needs to, but the speed of the boat will not inprove much. She will push a bow wave, raise her nose and double fuel consumption.

At 2800 RPM and 5.5 kts, she should hum along sweet as a single can and burn less than a quart an hour.

I could be wrong, but if I am, it's not by much.

05-29-2007 10:50 AM
USCGRET1990 Check out:
05-29-2007 10:38 AM
mwrohde Thanks for replying.

You're right - I want a 2-blade prop. I'm trying to do this as inexpensively as I can.

It's a RH prop. I'll measure the shaft tonight.

She's currently got a 14-10 as well. However, wide open under load I can only get 2500 RPM. My mechanic says that's due in part to having the wrong prop on there. He suggests a 12-12 or a 12-10. I've run the math, but my results are dubious at best, so I was casting about for a more experienced opinion.
05-29-2007 10:30 AM
JimsCAL Not a simple question! I am assuming you want a fixed two-blade prop, not a folding or three-blade. The key criteria are diameter, pitch, shaft diameter, and right-hand or left-hand in selecting one. Measure the shaft - it's likely 3/4 inch, 7/8 inch or 1 inch. Determine the direction the prop will turn when going ahead: clockwise = RH, counter clockwise = LH. Diameter and pitch are trickier. I would try to get a recommendation on these from someone who knows the boat. For reference my CAL 9.2 (30 foot) has a 14 inch diameter, 10 inch pitch folding prop which seems to work well.
05-28-2007 05:16 PM
Prop size?

Assuming I can get this *&%^ boat running again, what size prop is appropriate?

The engine is a Yanmar 1GM. Max RPM is 3600. Horse power is about 6.5. The gear ratio is 2.62. The boat is a Cal 27. 23'3" at the waterline. Displacement is about 5200#.

Thanks for your help.

Posting Rules  
You may post new threads
You may 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 On

For the best viewing experience please update your browser to Google Chrome