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Old 31 October 2010, 17:43   #11
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Quote:
Originally Posted by davej View Post
Have you checked that the small zinc trim tab under the cavitation plate is set at an angle to offset the turn?

Whenever this is serviced it needs to be replaced in the same position.

just a thought.

davej
This is definitely worth checking. If it's offset just centre/center/centaur it up and see if that makes any difference.
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Old 03 November 2010, 11:45   #12
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For Problem 1

Quote:
Originally Posted by GJ0KYZ View Post
This is definitely worth checking. If it's offset just centre/center/centaur it up and see if that makes any difference.
"just" centring it will be a bit of a difficult job if it is bolted to the transom! I know of a Ribcraft 5.3 with a 90 sat dead centre on the transom and no pull. My MErc & Yam were both dead centre, again no pull. My money is on your trim tab.

If you are trimmed too far out, the trim tab / skeg etc won't be doing what they should, and you end up with more of the opposing torque at the wheel (Newton's 3rd law - the prop shaft goes one way, so the rest of the engine wants to go the other way with equally vigour, and if there's no water stopping it at the bottom of the leg, it's all down to you on the wheel).



Problem 2)
When does it do this? If at speed in a straight line, and it happens at the slightest sign of a wave or a turn you are either trimmed too far out or may have a too small diameter prop.

There are small diameter big pitch props out there for lightweight boats, the idea being that you loose a bit of friction by reducing diameter, and load the engine back up with the relatively high "gearing" of the pitch & get more speed. Thing is if your engine was secondhand off a light boat (As my old Yam was) the prop will let go easily on a relatively heavy draggy rib. You may need to up the diameter & down the pitch if that's possible.

What RPM do yopu get at wide open throttle, and what is your current prop?
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Old 08 November 2010, 17:23   #13
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If you play with the trim and trip up a bit, then it either doesn't do it or does it less. Any thoughts?
therein lies your answer I would think. Trimmed in (down) a lot of boats will be heavy to steer and pull to one side so try it trimmed up a bit from your original problem area. You may need a stop in the frame to limit the trim's downard travel.
Trim up once on the plane on flat water. Trim down a tad for turns, after taking some speed off, so that the prop doesnt ventilate.

Be careful trimming down at speed as it can induce an unexpected and violent reaction esp if you have a heavy person on one side of the boat. Failure to trim down for turns can allow the back end to lose grip and then the boat may spin down onto its bow and cause major problems onboard.
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Old 08 November 2010, 17:54   #14
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Originally Posted by gotchiguy View Post
Jigsaw has an "off centRE" outboard
Are you the new spell-chequer?

Cheap dig, IMV
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Old 08 November 2010, 22:21   #15
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Are you the new spell-chequer?

Cheap dig, IMV
Funny, I didn't notice a spelling error... that's the way we spell it on this side of the pond. Don't worry G, in a couple of centuries you'll drop the french spelling as well.

It only makes sense to have the lettre appear where it's enunciated n'est pas? Novembre, Decembre etc.

As to the OP. Trim anode adjustment is all that's needed.
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Old 09 November 2010, 05:50   #16
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Funny, I didn't notice a spelling error... that's the way we spell it on this side of the pond. Don't worry G, in a couple of centuries you'll drop the french spelling as well.

It only makes sense to have the lettre appear where it's enunciated n'est pas? Novembre, Decembre etc.
Aww leave him alone, it's just his sense of humor
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Old 09 November 2010, 12:17   #17
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never found the trim anode to make any worthwhile difference in all honesty.
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Old 09 November 2010, 13:00   #18
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Have you tried moving the engine physically by hand, if you have NFB steering the wheel and engine won't move.
My mates RIB has "normal" steering and if you let go of the wheel and apply the power at standstill the wheel whips over due to the prop torque, as John said.
Not sure about cavitation, could be a whole load of things from driver error to the wrong prop?
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Old 10 November 2010, 11:04   #19
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in a couple of centuries you'll drop the french spelling as well.

It only makes sense to have the lettre appear where it's enunciated n'est pas? Novembre, Decembre etc.
Funny thing is, I'm quarter French. And sorry if I caused offence, I just don't appreciate Americanisation of words.
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Old 10 November 2010, 12:39   #20
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Quote:
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never found the trim anode to make any worthwhile difference in all honesty.
It does, but it's one of those things that works best at a given constant speed. Should be tweaked to minimize prop torque at your normal cruising speed.

Obviously, the tab will have little to no effect until you get a decent amount of water flowing around it, so it's not going to be too effective at low speeds.

jky
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