Prop for 8 HP Tohatsu and 26' sailboat - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance
 Not a Member? 
  #1  
Old 03-29-2011
tap tap is offline
Senior Member
 
Join Date: Apr 2009
Posts: 176
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
tap is on a distinguished road
Prop for 8 HP Tohatsu and 26' sailboat

I'm thinking of getting a high-thrust prop for my boat's outboard. The motor is a recent 4-stroke 8 HP Tohatsu and the boat is a San Juan 7.7, 26' LOA, 20' LWL and 3200 lbs design displacement. It has the standard 3 blade 8.5" x 7.5" pitch prop. Tohatsu has two high-thrust props available for the engine, 4 blade 8.7" in 5" and 7" pitch. Would either of these props be a better fit for my boat? And if so, which one?
Reply With Quote Share with Facebook
  #2  
Old 03-29-2011
tommays's Avatar
Senior Member
 
Join Date: Sep 2008
Posts: 4,215
Thanks: 1
Thanked 24 Times in 24 Posts
Rep Power: 6
tommays will become famous soon enough
The Diameter 8..26 x Pitch 5.9999 pitch worked well on my 4Hp pushing a 29' 8000# Cal 29 at 4.5 knots

I make a phone call to a place like InternetOutboards as the 5" may be a bit small
__________________
1970 Cal 29 Sea Fever

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

1981 J24 Tangent 2930
Tommays
Northport NY


If a dirty bottom slows you down what do you think it does to your boat
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #3  
Old 03-29-2011
tap tap is offline
Senior Member
 
Join Date: Apr 2009
Posts: 176
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
tap is on a distinguished road
My motor gets me up to speed fine. If my knotmeter can be believed I can just barely reach 7.00 kt under optimum conditions. Typical cruise speed would be around 6+ kt without towing a dinghy. I was hoping to get better control when docking and maybe better fuel economy with a high-thrust prop that hopefully slips less.
Reply With Quote Share with Facebook
  #4  
Old 03-29-2011
tommays's Avatar
Senior Member
 
Join Date: Sep 2008
Posts: 4,215
Thanks: 1
Thanked 24 Times in 24 Posts
Rep Power: 6
tommays will become famous soon enough
The HT prop pushes more because it allows the motor to reach its rated RPM at which point it makes 8 HP

You would need some type of handheld or tiny-tack to get and idea what RPM your reaching to make a good prop pick as i know even when pushing my J24 the stock prop was way to big and the HT one for the 4-6 HP series was massively better


I have never had a whole lot of luck with the stoping part using and outboard
__________________
1970 Cal 29 Sea Fever

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

1981 J24 Tangent 2930
Tommays
Northport NY


If a dirty bottom slows you down what do you think it does to your boat
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #5  
Old 03-29-2011
jrd22's Avatar
Courtney the Dancer
 
Join Date: Nov 2000
Location: San Juan Islands., WA, USA
Posts: 3,806
Thanks: 3
Thanked 14 Times in 14 Posts
Rep Power: 14
jrd22 will become famous soon enough
I have an 8hp two stroke Yamaha for our inflatable. I changed out the standard 8.5"X 7.5 pitch for a 6.5 pitch and we still get up on a plane and can do over 15 knots, so I don't think the 5" pitch would be too small for you at all.
__________________
John
SV Laurie Anne

1988 Brewer 40 Pilothouse

Reply With Quote Share with Facebook
  #6  
Old 03-29-2011
tap tap is offline
Senior Member
 
Join Date: Apr 2009
Posts: 176
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
tap is on a distinguished road
I have a Faria outboard tach that I can connect to my motor, but I haven't mounted it yet. For some reason anything that requires me to drill holes in my boat takes a really long time to happen. I'd also like to think of some way to only power the tach when the outboard is running without needing to manually switch it on and off. The outboard doesn't have remote controls so there's no ignition key that would be a natural choice.

My boat is very similar to a J/24. Same LWL and draft and it's only 100 lbs heavier. About a 1.5' more freeboard and beam though. So the 8 HP motor is more than adequate to move the boat, even if the prop isn't the right fit. I could probably make do with a 4 or a 6, but the 8 is what the boat came with. And I like the electric start and alternator, which I don't think you can get on anyone's 4 HP and I don't think the 6 HP tohatsu has a real alternator. The two cylinder motor runs smoother too.

I guess the idea here is that less pitch means the motor will run at higher RPMs for a given throttle. So the goal is to get a prop with a small enough pitch to develop the max rated RPM at WOT, so you get the rated HP out of the engine. What's the issue with using a prop that has too little pitch? The motor will over rev? Or that one will lose top end speed? Is the speed loss possible for a sailboat or is that something only planing boat would have to worry about. I know if you calculate the pitch x the RPM at the prop you'll get a speed far faster than a displacement hull boat could possibly go.
Reply With Quote Share with Facebook
  #7  
Old 03-29-2011
tommays's Avatar
Senior Member
 
Join Date: Sep 2008
Posts: 4,215
Thanks: 1
Thanked 24 Times in 24 Posts
Rep Power: 6
tommays will become famous soon enough
You only need to use the tack to test your current setup to see if can be inproved as going to to small a prop would make it worse and give you the abilty to run the motor at to MUCH RPM
__________________
1970 Cal 29 Sea Fever

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

1981 J24 Tangent 2930
Tommays
Northport NY


If a dirty bottom slows you down what do you think it does to your boat
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
tohatsu 3.5 won't run without choking jshep Gear & Maintenance 64 08-04-2012 08:26 AM
New Dink, Looking at Tohatsu 3.5 Sapperwhite Gear & Maintenance 43 06-30-2009 06:38 AM
Tohatsu 3.5 or 4 HP? galernikus General Discussion (sailing related) 15 10-26-2008 10:08 PM
Tohatsu 9.8 on a Chrysler 26 tlarndt Gear & Maintenance 1 11-23-2006 11:02 AM
Tohatsu 6hp 4-stroke? safarisurf Gear & Maintenance 3 07-06-2006 11:43 AM


All times are GMT -4. The time now is 08:03 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012