New prop causes veer to port - solution?? - 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 06-09-2008
Junior Member
 
Join Date: Oct 2000
Posts: 13
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
sailingdeacon is on a distinguished road
New prop causes veer to port - solution??

After years with an old 3 blade feathering prop, I replaced it with a new design folding prop. The new blade pushes the boat at higher speeds and has very little prop walk in reverse (right hand prop). The problem is that NOW under power the boat veers to port - significantly - and at the upper end of the speed range it is considerable. Max rpm under load is 2900-2950 of 3200 max - and the tac is correct. This 35' boat has no pull left or right if not under power. The shaft is centered and not angled either way. The rudder is perpendicular (to the eye at least) There is more than enough room between the prop and the hull.

It never did this with the old prop in any conditions - although at cruising rpms the speed was slower by about 1/4 to 1/2 knot.

After many emails with the manufacture, including photos, they are quite perplexed, but are suggesting a reduced pitch of 1 inch - which will get the rpms to max - at least.

Or would a reduction in the diameter of 15" be better??? Will the pitch reduction help?
Reply With Quote Share with Facebook
  #2  
Old 06-09-2008
djodenda's Avatar
Senior Member
 
Join Date: Mar 2006
Location: Kirkland, Washington
Posts: 1,557
Thanks: 1
Thanked 1 Time in 1 Post
Rep Power: 10
djodenda will become famous soon enough djodenda will become famous soon enough
What kind of boat?
__________________
David

1987 CS 36 Merlin "Kyrie"

"They drove a dump truck full of money up to my house. I'm not made of stone!" -Krusty the Clown
Reply With Quote Share with Facebook
  #3  
Old 06-09-2008
Capnblu's Avatar
Senior Member
 
Join Date: Mar 2006
Location: Squamish
Posts: 659
Thanks: 0
Thanked 4 Times in 4 Posts
Rep Power: 9
Capnblu is on a distinguished road
Steer to Starboard!
Reply With Quote Share with Facebook
  #4  
Old 06-09-2008
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
It would help if you said WHAT PROP YOU BOUGHT. Someone on the board may have experience with it... but if you don't say what brand, make and model it is, how can anyone help you???

It would probably also be wise to give the pitch/diameter of the prop as well as the type of boat and engine that you have.

I highly suggest you read the post in my signature... the more relevant information you can give generally results in better suggestions. As they say in the Computer Science field... GARBAGE IN ===>>> GARBAGE OUT.
__________________
Sailingdog

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

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Share with Facebook
  #5  
Old 06-10-2008
Senior Member
 
Join Date: Sep 2006
Posts: 2,179
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
Rockter will become famous soon enough
sailing...

If the pull is unacceptable to you, put the old prop back on again. Either that, or it's expensive trial and error. Finer pitch might help.
Reply With Quote Share with Facebook
  #6  
Old 06-10-2008
Idiens's Avatar
Larus Marinus
 
Join Date: Jan 2007
Location: Brussels
Posts: 1,756
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
Idiens is on a distinguished road
I observe the same effect on my boat since I re-engined and reversed the Maxprop rotation direction in the process. But on my boat, it shows itself more in terms of pressure on the rudder/wheel at high rpm. Since I adjusted the prop to give 3000 rpm at max throttle setting, but reach hull speed at about 2600 rpm and normally cruise at 2000 rpm, the effect does not worry me.
__________________
Jonathan-Livingston
Reply With Quote Share with Facebook
  #7  
Old 06-10-2008
beej67's Avatar
Senior Member
 
Join Date: Apr 2008
Posts: 257
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 7
beej67 is on a distinguished road
Quote:
Originally Posted by sailingdog View Post
GARBAGE IN ===>>> GARBAGE OUT.
Yeesh, Dog, a simple "Could you be more specific?" would have probably sufficed.
__________________
beej67, Checkered Past, 1980 32' Pearson 323, Panama City FL
Reply With Quote Share with Facebook
  #8  
Old 06-10-2008
Junior Member
 
Join Date: Oct 2000
Posts: 13
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
sailingdeacon is on a distinguished road
I doubt naming the prop will help since there was only one brief response to my query here for any experience with the prop sometime ago (Search on Slipstream prop) . I did not describe the specifics since the theory of what causes a prop/boat to act like this is generic in my opinion. However here are the details:

It is a relatively new design, "Slipstream" folding 2 blade prop made in Australia. the boat is a 1987 Ericson 34 shoal fin keel, exposed rudder with a the prop a large distance from the keel and rudder. (photos are available but will confirm this) It is a 15x9 prop. Engine is a Universal M35 4 cyl 30 hp engine 1.8:1 reduction. Mounted on the center line. Rudder is perpendicular and is a balanced spade rudder. Boat goes straight under sail with no wheel pull.

Former prop was an older model 3 blade feathering prop. I sold it since I would stay with the better performance of this prop even with the problem, but I am not certain if a prospective buyer would agree. The new prop gets 2950 of 3200 rpms. no smoke, no overheating.

I now get 6 kts at 1800-1900 rpms, with a noticable pull on the wheel to the left (with the boat wanting to go left). At 6.5 at 2300 rpms the pull is very considerable.... In either case if I let go, the boat goes quickly to the left in a tight circle - hardly a safe situation. These rpms/speed are about 1/4 to 1/2 knot faster than before

BUT the powering performance is truly superb - I would not trade it.. and of course when racing the folding prop is as expected. There is no noticable prop walk in reverse and the stopping ability is quite sufficient. In general a very superior folding prop.... except for this one problem. The manufacture has been very helpful but has not run into this before after many sales worldwide... although the problem in general is not unheard of. He says various subtle factors can be working... placement of the zinc, distance of the prop from the boat fore and aft, etc.

So he is supplying relpacement 15/8 blades (just have to replace the blades, not the core) which will get the rpms up to 3200 max and hopefully will help. But it requires a haul out because of the use of duplicate set screws using loctite as a final backup. It will be next year before my normal haulout and I would pay for a haulout now if the problem could be resolved. (my wife is not fond of holding the wheel under pressure while motoring)

I suppose my concern is that with a reduced pitch, I might get the same degree of pull at the same speed as before (while at a slightly higher rpms). Since I would like to go 6 to 6.5 knots, there might be no real changed in the pull. Or will there be a change??? Or would a reduced diameter be better... as my local marine mechanic says.

One Internet resource indicates that with power boats at load speeds, an over pitched prop will cause the boat to turn. But that is mainly a power boat web site.
Reply With Quote Share with Facebook
  #9  
Old 06-10-2008
Idiens's Avatar
Larus Marinus
 
Join Date: Jan 2007
Location: Brussels
Posts: 1,756
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
Idiens is on a distinguished road
I suppose a two bladed prop could have a more pronounced effect than a three bladed prop when absorbing the same power.

I presume the effect is caused by the flow from the propeller being a spiral and hitting the rudder at two different places, high and low, in opposite directions - from a centre of pressure point of view - i.e. the left turning moment is greater than the right turning moment on the rudder.

A skeg would perhaps help reduce the effect. With a balanced blade rudder, one would need to correct the balance with regard to the prop flow. That implies a new rudder design.
__________________
Jonathan-Livingston
Reply With Quote Share with Facebook
  #10  
Old 06-10-2008
retclt's Avatar
Roadkillibus Texanis
 
Join Date: Nov 2006
Location: Great State Of Texas
Posts: 1,602
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
retclt will become famous soon enough retclt will become famous soon enough
Quote:
Originally Posted by sailingdog View Post
It would help if you said WHAT PROP YOU BOUGHT. Someone on the board may have experience with it... but if you don't say what brand, make and model it is, how can anyone help you???

I highly suggest you read the post in my signature... the more relevant information you can give generally results in better suggestions. As they say in the Computer Science field... GARBAGE IN ===>>> GARBAGE OUT.

Lighten up Francis!!! Geez.


Adding a trim tab to the rudder would do the trick but when not under power you'd have to adjust. No advice here . . . I just wanted to tweak SD since I'm negative proof now.
__________________

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



Bob T

"I cannot not sail" - E. B. White
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
Number of race entrants up from 2006 - Port Huron Times Herald NewsReader News Feeds 0 07-16-2007 07:15 AM
Changing prop underwater trantor12020 Gear & Maintenance 16 03-03-2007 12:02 PM
Max prop on a saildrive levenezia Gear & Maintenance 16 09-20-2006 12:07 AM
Choosing the Right Propeller Sue & Larry Gear and Maintenance Articles 0 02-04-2003 07:00 PM
Choosing a Prop Sue & Larry Gear and Maintenance Articles 0 12-24-2001 07:00 PM


All times are GMT -4. The time now is 03:44 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