Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Pleasure boats, Sports, Race, Power and Leisure Boats: => Topic started by: supersonic on October 14, 2007, 03:04:00 pm
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Hi Guys, Can anyone throw some light on my problem please ?
wood hull huntsman 31, fitted with 7.5 nitro direct drive,standard large rudder.1818 prop
When the boat comes up on plane, I can steer in a straight line but the boat leans to the starboard side.
I have plenty of weights in the bottom rear because the engine is mounted slightly forward.I .have tried the weights
in the port side but without improvement.Is it the torque of the prop that may be causing this ?
Any help would be appreciated.
Dave.
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Sounds like torque reaction, pair of trim tabs would probably help. 'In the olden days' those kind of craft were often fitted with a wedge just on one side at the transom to counteract that condition.
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Thanks Grasshopper, I will try that, but do you think a smaller prop but bigger pitch would have any effect ?
Dave.
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Also, just check everything is straight.
Get the boat on the plane and set the rudder and trim so the boat is going dead straight with hands off ( easiest when boat heading directly away from you). Bring the boat in and check if the rudder is off set. If it is, the rudder maybe acting slightly like an aeroplanes aileron and causing the boat to lean.
If it is torque, try a smaller propeller.
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Thanks Martin, The boat does run straight and comes on plane easily , It has not been on full throttle yet (new engine).
dont want to over-rev it so I have a smaller prop with a lot more pitch, I will try that,
cheers
Dave.
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Hi supersonic,
What length is the boat, as the motor sounds a bit on the large size if it's the thirty six inch model. Also this happens with a deep v hull. At speed the hull will be well out of the water so there is very little cross section to keep it upright. As you already suspect prop torque is responsible, I don't think that down sizing diameter and increasing pitch will help much if it achieves the same thrust, as in theory (at least in my head) torque will be the same. I would try the trim tabs or wedge as already mentioned.
Bob
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Bob,The hull is huntsman 31 (34 inch) fitted with a Leo 46 without tuned pipe, can be viewed on video in
sports boats etc under huntsman build. You can see the lean about halfway thro the video
It would be difficult to put trim tabs on the transom and I think it would spoil the lines of the boat .
The wedge advice seems to be the way to go, and this being new to me I suppose I could experiment
with a wedge and some duck tape.
thanks for your input
Dave
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Hi again,
Utube looks good. I can assure you that compaired to the fast Swordsman/Huntsman in our club, you don't have a problem. The one in our club literally runs on the side of the hull. Also the props usually tend to come out of the water on the turns.
I realise what you mean about the trim tabs, as your boat has a curved transom. You could try temporary fitting of wedges using double sided tape.
Bob
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The full-size boats had trim tabs, and they needed them. Have a look on the Fairey Owners Club website.
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Thanks Jonty, interesting site that, Going to try a Balsa wedge next time out !
Dave.
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Been hunting for some photos of Point One, my father's Swordsman 42. No luck, I think they must be in France. That boat had hydraulically powered trim tabs. Depending on speed, wind, and currents they needed frequent adjustment to keep the boat just right.
I see that some of the continental model boat racers have a similar system with a servo for each trim tab.
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Hi, Jonty, Great afternoon -Saturday took the huntsman to the lake with your suggested wedge fastened under the transom
with tank tape. a great improvement on its previous run. Thanks again for that ! Next time I am going to shorten the prop shaft by about an inch which will move the prop forward and hopefully feed more water under the back of the boat and perhaps make for more stable turns. O0
Dave.