turning issues

[talbot.s]

I have a question for all in the know. I have an 18'x60" center console flat inboard, for lack of a better word, with issues. It does not turn very well. It does not lay over on its side as a good planing hull should in turns. Calculating the center of gravity at around 14.5'. Would moving it forward help any? what other options would ya'll recomend? thanks in advance.

[TerryKing]

Is this a 'straight' (Fixed prop shaft) inboard?

What is the rudder location and shape?

Is there a significant keel / skeg? Any other bottom features??

Does it turn a lot different to port than starboard?

[Guest625101138]

I gather you are saying it is flat bottomed.

If this is the case then the hull does not provide much lift on the outside when you go into a turn as you get with a 'V' bottomed boat. In effect you turn by pushing the stern sideways.

If you turn hard at speed there is a risk the chine will bite and you will actually flip it. I have done this with a very early Dehaviland aluminium hull that was driven by a 10HP outboard. Obviously lighter than your boat but also likely to be less power and much slower.

I do not know if you can add any lifting surfaces that would improve the situation.

Rick W.

[Frosty]

Rick is correct a flat bottomed boat will not turn correctly. It is likely it was never intended to plane because it will not turn,-- ever.

UNLESS, if it is an inboard with shaft, you could fit a long rudder this would try to force the outer chine up and with a bit of luck above the water line.

Or if its an outboard a similar effect could be gained with a long shaft.

But to be honest I am taking guesses here because its not the right boat really.

[talbot.s]

The boat has a homemade areneson SP? drive and "ice runners" with 4" skegs towards the stern to hep it track straight and turn. The boat is designed to run fast in shallow water. It is a relatively common design and most of the other boats do not have this problem. The drive is all stainless and weighs 159lbs attaching to the transom and sticking straight out the back. Same turning port and starboard the boat starts to bite then slides over the "hump" till the chine bites then continues the turn, scary. Boat has a 351 ford, 1:1, 14.5x14 prop turning 4700 WOT.

[TerryKing]

The boat has a homemade areneson SP? drive and "ice runners" with 4" skegs towards the stern to hep it track straight and turn. (snip)...

To turn, the aft end has to be able to move sideways a little.

I believe you have too much area in the 'ice runners' and skegs and they are overly effective in keeping the boat straight.

I addition the Arneson type drive (does it have a rudder section at all?) does not give the "below the CG" torque to rotate the hull in roll into the turn, like a conventional rudder. The main force that causes a powerboat to roll in the direction of the turn is the side force applied way below the waterline by the conventional rudder or outboard or I/O drive/skeg.

I had a similar problem with a 17 foot straight inboard I built many years ago. I had two long 'ice runner' type keels on the bottom, only about 2 inches high and 4 feet long.. Didn't seem like much, but it kept the aft end from moving sideways. I cut them down to 1 foot long and the boat turned much easier.

Your straight-line stability features seem to be working all too well..

Other: Can you post any details of your surface drive? I and others are looking at building them outselves....


We're all learning stuff here.

[talbot.s]

Before I put the runners and skegs on the boat would just slide, very similar to an airboat with a slick bottom. After the runners and skegs it helped considerably but it seems like it's not enough or that its a weight or design issue. I did not run the runners all the way to the bow, only to about 1 ft forward into the transition. www.ronniesairboats.com look at the mudboat links.

[TerryKing]

Before I put the runners and skegs on the boat would just slide, very similar to an airboat with a slick bottom.

Perhaps you just overdid it a little...

Some racing boats have a short skeg that is located 3 or more feet forward of the transom. I think that allows the boat to yaw about that point so it can turn... If it was all the way aft, it would be hard to turn.