New boat pulls to starboard under power, prop?

[Suijin]

Originally Posted by a64pilot

What contributes more to "prop walk" pitch or diameter, I'm thinking it might be pitch, but I'm also thinking in reverse too.

That's an interesting question, and I don't really know the answer for sure but I'm going to guess that they contribute "equally." It's a question of the more "aggressive" side of the biased propeller moving more water than the other; both diameter and pitch contribute to that. So, any combination of diameter and pitch that puts the proper load on the engine is going to move the same amount of water...decreased diameter and increased pitch, or increased diameter and reduced pitch.

[cal40john]

Looking at where the rudder post goes into the rudder, that doesn't look like there is much in the way of a balanced rudder.

[brightontrader]

OK OK so much return information and thanks to everyone who has taken the trouble to reply.

I was offline yesterday talking to a propeller guy (Sillette) and the original owner about hard specs. (The Sillette man said that he had come across boats that there was no cure for.....purely hull design was flawed and that production boat designers worked through these potential issues before making a mould....and one offs could suffer this......ooops.)

Anyway::

Engine is 85HP John Deere with 2.94:1 ratio box. Prop is 26:16. Boat weighs around 21 tons all up with about 38' of water line.

One poster suggested I run the boat at 1/2 power, yes there is no noticeable pull at this speed but I have sailed the world once already on my old boat (very similar design boat, also steel pilot house one off with an 85HP but much smaller prop from memory) and there were many times I needed near full power for long periods, to get off bad rocky coasts, through Gib straits in a Levanter etc.... and many times like Atlantic with no wind just ticking over with sail and engine..but with this boat I want it right. (I am a motorsailer by nature, I like electricity powering all systems. )

The boat though has a generator attached to the shaft and the previous owner said that he put on a big prop to drive this and that he thought it was too big.

I am going to hire a naval architect to do the calculations, already been in touch with Angram in Shoreham in Sussex, before I do anything drastic......but am grateful for the suggestions but still extremely worried...

Will post results.....

[wellin]

Originally Posted by jldunn86

My .02$,
Set the autopilot to a rudder trim tab to drive the balanced rudder. This has been accomplished successfully on many sailing boats and works fine while under power as well. Driven by either wind vanes and/or smaller ram drives. The smaller rams use less energy.
Regards

This is how large airliners are flown. The pilots controls work a small tab that moves the large surface.

Sent from my SCH-I415 using Cruisers Sailing Forum mobile app

[hpeer]

Originally Posted by Reefmagnet

Perhaps engine and shaft alignment is worth checking. Our boat had a terrible pull when we first purchased her, which I assumed at the time was prop walk. Discovered post delivery that the so-called professional that installed the new engine for the PO's had forgotten to adjust the rear engine mounts and must have only finger tightened the front mounts. I replaced the rear mounts and realigned the engine and shaft and the constant pull under power stopped.

Yeah, I developed a strong pull last summer. Over winter found a broken engine mount. Replaced mounts and realigned ( new shaft, cutlass, recondition prop, drive saver) and now the pull is gone.

[brightontrader]

Hpeer, sounds expensive, didn't you feel the mount had gone?

In my case this pull is from launched as far as I can tell from Previous O.

Still hoping its just an oversized prop and not something more, or worse, not fixable.

[delmarrey]

I haven't read the whole post but the first thing I noticed in the picture is that the prop is very close to the transom along with a Conoe stern. IMO that doesn't give the boat hull much resistance to prop walk. Which makes it a poor motor sailer. If it were to have a smaller rudder it would be even worse IMO.

[carstenb]

Stop and think a minute about propwalk.

We're all in agreement that with a clockwise turning propeller (going forward) the stern will move to port when put in reverse.

The OP complained about the boat pulling heavily to STARBOARD when going forward.

Sorry - that is not a propwalk issue. A boat with a right hand propeller, going forward will pull to PORT. Think about it. Going backwards, the prop pulls the stern to port. Going forwards - the prop pulls the stern to STARBOARD, causing the bows to go to PORT.

It is not propwalk.

Lots of other potential causes though, bad alignment, æoose engine mounts etc etc.

For those that need a practical example. Tie your boat to the dock at the middle of the stern, put the engine in forward and watch the stern move to starboard and the bows move to port. Or go out on a day with no wind or current, sail on the engine, engage the autopilot and watch to which side the autopilot moves to correct for the propwalk - correct the autopilot will turn the rudder to compensate and the rudder will be turned to STARBOARD.

[hpeer]

Originally Posted by brightontrader

Hpeer, sounds expensive, didn't you feel the mount had gone?

In my case this pull is from launched as far as I can tell from Previous O.

Still hoping its just an oversized prop and not something more, or worse, not fixable.

Unbelievably the mounts were installed not on top of the stringers but underneath, with big holes in the metal so that the mounts stuck up through thee stringers. It also inhibited their movement. 32 years like that.

It's fixed now with a normal mount.

I think it was just all normal wear and tear on an old boat. Hopefully it will last another32 years.

[Cadence]

Originally Posted by brightontrader

OK OK so much return information and thanks to everyone who has taken the trouble to reply.

I was offline yesterday talking to a propeller guy (Sillette) and the original owner about hard specs. (The Sillette man said that he had come across boats that there was no cure for.....purely hull design was flawed and that production boat designers worked through these potential issues before making a mould....and one offs could suffer this......ooops.)

Anyway::

Engine is 85HP John Deere with 2.94:1 ratio box. Prop is 26:16. Boat weighs around 21 tons all up with about 38' of water line.

One poster suggested I run the boat at 1/2 power, yes there is no noticeable pull at this speed but I have sailed the world once already on my old boat (very similar design boat, also steel pilot house one off with an 85HP but much smaller prop from memory) and there were many times I needed near full power for long periods, to get off bad rocky coasts, through Gib straits in a Levanter etc.... and many times like Atlantic with no wind just ticking over with sail and engine..but with this boat I want it right. (I am a motorsailer by nature, I like electricity powering all systems. )

The boat though has a generator attached to the shaft and the previous owner said that he put on a big prop to drive this and that he thought it was too big.

I am going to hire a naval architect to do the calculations, already been in touch with Angram in Shoreham in Sussex, before I do anything drastic......but am grateful for the suggestions but still extremely worried...

Will post results.....

You have peaked my curiosity. I am making the assumption that Deere is a is a 4045 with a 2500 RPM continuous ? What is your speed made good at that RPM? I won't throw a bunch for nos. out. I would like to be able to determine your slippage.

Someplace the thread took a short side track about shaft dia.. What is hers?

Looking forward the architect's feedback.

[Lodesman]

Originally Posted by brightontrader

Just bought a 46' fin keel, balanced rudder steel motor sailor with a 26" 16" pitch prop that under power pulls considerably to starboard, so much so on the delivery trip in strong seas burnt out the autohelm driver motor.

.

It might be the perspective of the photo, but it looks like the prop is on backwards.

[carstenb]

Originally Posted by Lodesman

It might be the perspective of the photo, but it looks like the prop is on backwards.

Damn. You know I think you are right

[Lodesman]

Originally Posted by carstenb

Stop and think a minute about propwalk.

We're all in agreement that with a clockwise turning propeller (going forward) the stern will move to port when put in reverse.

The OP complained about the boat pulling heavily to STARBOARD when going forward.

Sorry - that is not a propwalk issue. A boat with a right hand propeller, going forward will pull to PORT. Think about it. Going backwards, the prop pulls the stern to port. Going forwards - the prop pulls the stern to STARBOARD, causing the bows to go to PORT.

It is not propwalk.

.

From the picture, it looks like a counter-clockwise prop.

[SVTatia]

Originally Posted by Lodesman

It might be the perspective of the photo, but it looks like the prop is on backwards.

Originally Posted by carstenb

Damn. You know I think you are right

I hope you are being facetious.... I defy anyone to install a prop backwards.

[SVTatia]

Originally Posted by jldunn86

My .02$,
Set the autopilot to a rudder trim tab to drive the balanced rudder. This has been accomplished successfully on many sailing boats and works fine while under power as well. Driven by either wind vanes and/or smaller ram drives. The smaller rams use less energy.
Regards

Easier said than done. The challenge is to mount the autopilot to the trim-tab arm. I tried this on my steel boat, and used 3 kinds of auto pilots without success - the arm moves very little for a big affect on the rudder and the autopilot almost broke the entire structure trying to correct and waiting for the boat to respond. This could work on fiberglass boats but not on steel ones.