Prop to hull clearance - SailNet Community
 
LinkBack Thread Tools
post #1 of 5 Old 11-15-2010 Thread Starter
Junior Member
 
Join Date: Apr 2010
Posts: 19
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Prop to hull clearance

I am currently repowering my 2I8 with a Beta 20. This of course requires a new prop also. The old MD7A had a 12" prop installed. The clearance between the prop tip and the hull is about .5". I read that prop tip to hull clearance should be 10% to 15% of prop diameter. So, my question, what have others who repowered done in this area? Did you just stay with the 12" prop or downsize to an 11" prop? Has anyone noticed any problems with less than optimal tip to hull clearance?
Thanks for any input,
Paul
28islander is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 5 Old 11-15-2010
Member
 
jb1528's Avatar
 
Join Date: Nov 2010
Location: Mukilteo WA
Posts: 59
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 5
 
Prop to Hull clearance

Paul,

I can't speak directly to the Islander clearance, but I believe that the percent of diameter is a good. My friend who did his cutlas bearing had to shorten his propshaft for some reason because of something unrelated. He took out a spacer or some darn th ing. Anyway, the result was a close tolerance between the hull and prop. He experienced a vibration he didn't have before and perhaps slightly less efficiency because of it too I believe.

Clearance is good.

Jim
jb1528 is offline  
Quote Quick Reply Share with Facebook
post #3 of 5 Old 11-15-2010
Senior Member
 
DelmarRey's Avatar
 
Join Date: Aug 2001
Posts: 258
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 14
 
Dave Gerr gives the following values in the propeller hand book.
Minimum clearance of the propell diameter:
RPM 200-500 S/L less than 1.2 = 8%
RPM 300-1800 S/L 1.2-2.5 = 10%
RPM more than 1000 S/L over 2.4 = 15%
Planing crafts S/L over 3 = 20%


More sources:

propeller clearence

"Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful!"


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
DelmarRey is offline  
Quote Quick Reply Share with Facebook
post #4 of 5 Old 11-15-2010 Thread Starter
Junior Member
 
Join Date: Apr 2010
Posts: 19
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Yes, I have read the references on proper tip to hull clearance. Hence the questions I posed. I was hoping to get a response from other 2I8 owners who have repowered. I suspect they have the same issue and was wondering how they dealt with it and/or if they noticed any issues with the 12" prop and the stock shaft/strut setup. I would think all 2I8's have the same setup. The original setup on my boat only had .5" clearance and was like that for 33 years. Maybe it is a non-issue.
Paul
28islander is offline  
Quote Quick Reply Share with Facebook
post #5 of 5 Old 03-13-2011
Junior Member
 
Join Date: Mar 2011
Posts: 25
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Paul,

You've probably already figured this out, but I just got back on the Sailnet forum and thought I'd chime in since I replaced the prop & shaft on Opti during haulout back in Fall of '09.

On this project I replaced the original fixed blade prop with a Martec folding prop, hoping for better sailing performance and reduced prop-walk in reverse. Clearance for the original prop to hull was 1/2". We decided to move the prop towards the leading edge of the rudder to increase the hull clearance, all calculated prior to cutting & threading the new shaft. I have a photograph, but can't figure out how to post. (???) Any help for a 'newbie' to the site would be appreciated.

BTW - close-winded sailing performance in heavy weather was greatly improved with a folding prop. Disturbed waterflow coming from the fixed prop was separating as it streamed along the rudder, resulting in loss of tiller control at high degrees of heel/speed. With the folding prop, flow is more laminar across the rudder, providing a dramatic increase in helm response at the tiller.

Forward motor thrust hasn't been noticeable, due to the already very underpowered MD6B pushing her along. Reverse is slower to engage, thrust is much lower, but once reverse movement starts I have helm control. Which has been very helpful in docking. ~Joel

S/V Optiminium
1976 2I8
joelozzy is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

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

Password:


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

Email Address:
OR

Log-in









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.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Bridge clearance on ICW Pamlicotraveler Cruising & Liveaboard Forum 30 09-07-2011 04:43 PM
Seidelmann prop-shaft through hull Ham1sh Gear & Maintenance 2 04-20-2010 11:21 AM
Under Keel Clearance JustSomeGuyinDC Cruising & Liveaboard Forum 15 01-31-2010 05:17 PM
Rudder clearance steveg353 Gear & Maintenance 0 08-21-2009 03:15 AM
Question on fixed prop drag / hull speed Northeaster Gear & Maintenance 5 04-12-2007 07:26 AM

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On

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