Prop Torque Question

[aztec]

I have a Loftus bennett 17ft fast fishing boat with a 60 hp Johnson VRO on the back.

It used to have a 48 Mariner untill the gearbox failed.

My problem is that it's stable at about 23Knts although the helm is heavy. The closer I get to 27 Knts the more unstable the boat feels and has a list to stbd (this is worse when wind is on the stbd bow/qtr)

I have decreased the pitch on the prop as the origional was 21 (now 19) to allow the engine to rev a bit more, didn't seem to make any difference. the engine trim is manual adjustment only, this too has been played with to get the best ride.

My question is one of should i consider trim tabs, or do you think this is a anode tab adjustment??

Over to you..

Thanks.

 

[spannerman]

The trim tab anode will just give you even steering with no pull to one side, but this only works in a narrow speed band and not all through the range as you will find out if you adjust it. So optimise it for your normal cruise speed.
The heeling will be cured by fitting trim flaps, as it is a typical planing hull characteristic to lean into the wind, the bow is being blown downwind and you correct with the steering so the boat naturally heels into the turn which is cancelled out by the side wind so the boat runs straight albeit with a lean to windward.

 

[aztec]

Thanks

Awsome reply, and what's more makes absolute sense.

never come across this before, i guess my boats were always too big or too slow!

I like this one as it goes like a convent girl being harressed by several tramps.

Thanks.

 

[MapisM]

Careful there.
Spannerman is right, but the trim tab anode does just what he said - compensate the pull on the steering wheel.
Which with a normal r/h prop, and no correction, means that you should feel more resistance when steering to port (or that the wheel should "pull" to stbd, in other words).
I'm not sure this is what you're experiencing.
On one hand, that has nothing to see with the listing, and otoh you were talking of instability, rather than a tendency of the boat to steer to stbd.

PS: of course the above should be read the other way round if you have a l/h prop, though that would be very unusual on a single outboard.

 

[Spi D]

Pictures not copied, post is from worldseafishing.com:
http://www.worldseafishing.com/forums/showthread.php?t=99306

along the menai straits and spotted, in a back garden
-PICTURE-


Managed to find the owner and was very impressed with the "look" of the boat. Did some homework and found out it was a "loftus bennet" , the boat was made in two guises......16a being the shorter and the 16b having the benefit of a galley area..........after many hours of refurbishment I replaced the windows with Plexiglass ( the remains of which are for sale on site), I am a car body repairer and so completely overhauled the boat, to the standard I would like to buy one in....



My Local launch site was underneath the Menai Bridge ..........up I went and in the boat went



I used this boat for quite a while and NEVER managed to stop it going where it wanted , the front end seemed to be on another planet.....hit a wave and off it would go in any direction other than that in which it was previously heading. I tried all manner of things to cure it ,nothing made any difference.
With a 70Hp on the transom it would manage 30 knots but only on a flat calm, try it on anything other and you would be in trouble, I nearly got thrown overboard whilst flat out and hit a small wave, the boat veered off to the left and I very nearly went over the starboard.

The boat was designed for river / canal / inshore use...............it is not to be trusted.............

Apologies for the picture quality, I just took them from my album using my mobile.........

 

[aztec]

that sound just like my boat!

bloody mind of its own. not come across charechteristics like this before.

Should be a fast hull, everything is there, but practically she's a right handfull!

That's why i was thinking trim tabs, to give her some stability

 

[burgundyben]

Hello! Long time no see!

What happened to the Osborne?

 

[longjohnsilver]

Hello! Long time no see!

What happened to the Osborne?

Hey BB you just beat me to it! Good to see you back Aztec, how's life down Wareham way?

 

[aztec]

Hey BB you just beat me to it! Good to see you back Aztec, how's life down Wareham way?

Hi both!

Ah the saga of the Osborne!

Well...

Got myself divorced (partly due to the boat i think!) and bought another house... boat was ashore for 4 years costing me a fortune so couldn't afford to do "stuff"....

Bought another house (with a big drive) and shortly before christmas this year, moved her to her new (temporary i hope) home in Poole.

Got my self re married (don't say it!) to a lovely lass who's into boats as much as i am (BB - got one of them saily things down in hythe)

So after a bit of cleaning and general time wasting, i'm back to the restoration bit. Engines are waiting to go in, and due to the time in the boatyard i have to do some repair work on the nice new decks.

Other than that most of the other work is done. Not kidding myself this time, i'm hoping for a 2013 launch.....

Hmmmmmm wonder if we could resurrect that old party idea??

Hope all is well with you's and yours, and look forward to some of the most brilliant boaty banter once more.

Steve.

 

[longjohnsilver]

Good to hear life's better. Are you still putting out fires?

 

[aztec]

Good to hear life's better. Are you still putting out fires?

Sort of.

I work at our training centre teaching others to put them out!

My main subject is road traffic collision. so cutting up cars for a living... can't be bad eh?