Performance/Handling Problem

[Boa]

I have a 22' speedboat, medium deadrise, with 2 x 100hp Yam 4 strokes mounted on outmounts on the back.
There seems to be a problem in the handling/performance of this boat. From 1800rpm the trim is normal, then when speed is increased the trim increases radically and the boat drops/heels over to the starboard side (and it is always to starboard). It will only come back level when you throttle back, also no amount of motor trim will help the situation at speed.
What could the problem be, a combination of weight distribution and suction on the starboard hull bottom (due to a hook or unfairness) or something else?.

[yokebutt]

Hmmmm....Veeerrry interesting.....

Well, just pulling a loose idea from 'twixt my buttocks here, but could it be excess fore-and-aft convexity on the starboard side perhaps? (easily checked with a long ruler)

Have you tried bringing a couple of bubbas on the boat and moved their weight around? That might give you some clues to what's going on.

Good luck,
Yoke.

[KCook]

Has the boat always done this, or is this a new problem? Could be an error in the rigging of the outboard motors. Not just the right height or other mis-alignment. Also might be a propellor problem. Such as one hub is spun, etc. Dumb stuff, I know, but you have to start somewhere. There are also lots of guys with twin outboard experience on the forums over at www.TheHullTruth.com

Kelly Cook

[gerard baladi]

Twin Yamaha 100 HP / propellers rotating in the same direction. try offsetting the left engine to counteract and see what happens

[nevd]

I assume both motors have same prop rotation as I doubt counter rotating are available on this engine. The fact that the listing is to starbd indicates it is not motor torque as that should cause the port side to run low.

As recommended in an earlier post, you need to check for buttock straightness - compare each side. You should also check the curvature in the bow area (compare one side to the other) up to the point where the bow is touching the water when you have the problem.

[Boa]

Yes, the props are both clockwise/right handed and this particular boat has always had this problem. Will check the running lines with straight-edge to check for hollows. What would the reason be for the excesive longitudinal trim that can not be gotten rid of with the trimming planes.

[nevd]

Listing to starbd could be because there is more curvature on starbd side than port side creating suction on starbd side - this will also get worse as speed increases. The port side may also have a hook near the transom.

The other cause could be the hull has higher effective trim angle on the port side because of distortion of the hull.

All these problems could have been from initial manufacture or they could have been generated by storage or trailer problems.

Whilst not very likely, you should also check to see if the problem is decreased by increasing the throttle opening on the starbd engine as there may be engine differences or engine mounting errors.

[Willallison]

There was a very good article in Proffessional Boatbuilder some months back - I think by Donald Blount that covered the topic of dynamic instability very thoroughly. It might pay to get hold of a copy ( available from www.proboat.com ) and see if any of the issues raised there are applicable to your boat

[ljwhisenant]

mount a hydro stabolizer on your power boat they are pretty cheap also simple to mount.

[ccb]

would trim tabs solve the problem of listing at speeds

[Boa]

Yes the boat has trim tabs but they have not helped at all.

[chumnuts]

get the boat on plane and try each motor seperatly. My 30' midnight express also has 2 right hand motors. Same problem around 55 mph.When I throttle up I always give the star motor a little less. One more thing I did to help was the anode above the propeller (the fin) was straight and needed to be turned a little outboard those things compensate the prop turn. And they really work. If your motors are placed really far apart from each other this might also not help. Try to find a counter rotating lower unit. And swap.