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Old 11 September 2004, 23:13   #1
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Country: USA
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Boat name: Stormy I
Make: Airsolid
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Need for speed vs stability

I have a 20' RIB with 115 Yamaha 4 stroke. My hull weight is 312 kilos + engine + me. I am getting chine walk around 43-45 mph and am wondering if the position of my helm has any impact on stability. It is close to the stern. I am wondering if I moved it forward, what if anything, that would do to the handling and stability. I am running at 3/4 throttle at 40 mph and would love to let it out without winding up in the drink.

I am new to RIBs and have no resources or other RIB owners around (U.S.) other than those used as tenders.

Any comments appreciated. I will try to attach a pic, but not sure if that will help. Regards...
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Old 12 September 2004, 03:35   #2
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Hi, Stormy! It is normally two things you can do, weight up front and/or look at propeller.
A propeller might do very much for the boat.
A racingpropeller might lift the bow to get more speed. Some propellers lift front or rear, and some does not lift at all.

When it comes to weight in front, there have been written many pages about the theme here on rib.net, just search.
They might tell you to try moving everything, console, battery, gastank, put 2 double jockeyseats in front and put people on them, they will have a great and safer ride instead of sitting on the pontons, which by the way is dangerous.
Best regards
Martin
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Old 12 September 2004, 04:16   #3
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Fill some 5 gallon barrels with water and strap them to you deck in various places to simulate different layouts. Take her out and see if there's a difference!


Andy
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Old 12 September 2004, 09:51   #4
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Country: USA
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Thanks Andy and Martin for the suggestions. I will investigate the props and weight distribution suggestions. Any ideas on the way to reduce chine walking (tendency to go side to side at high speeds) or is that just the nature of the beast? Regards.
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Old 12 September 2004, 14:20   #5
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It is often caused by having the bow trimmed up too high (engine trimmed out too far ). Play with the trim a little it may be just a matter of very fine adjustment downwards/inwards.
It's a fine line between optimising the trim for speed...when the boat may become twitchy....and making it more stable and predictable but losing a couple of knots.

If I am using a boat for the first time I will usually get the engine trimmed out as far as I can just to the point where the stern gets twitchy and then just knock the trim down gradually until it stops.

However....all boats are different and some respond to this more than others.

Experiment with the set up and controls you already have before moving things around is what I would suggest.
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Old 12 September 2004, 15:43   #6
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Is the chine walking at max revs or are you stopping at the Chine walk stage (and I don't blame you for that) and have more revs left if so how much.

The boat seems quite light for a 6 m boat!
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Old 12 September 2004, 22:17   #7
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Country: USA
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Rogue and Robin,

Thanks for the reply.

Answers to your comments:

Robin: I have not tried what you have suggested, but will give it a try in the a.m. and report the results.

Rogue: I am shuting down at the point of chine walk, my revs are 5000-5100 and have plenty of room for more, just too old and the waters are too cold to see if I can push through or beyond it. The boat is from a small builder in Montreal. The Montreal police and rescue have been using the boats for 8 years and stand "high" on their performance and "sea ability"



They took me on 2 "drill" runs on a 24' powered with twin 250 hp's. In 1-2 meter following seas we sustained 33 knots with impressive performance. I do not know enough about RIBs to ascertain if the boat is too light or not. In the test run of the sistership we maxed out at 56 mph with the identical configuration in a flat sea. I did not notice any chine walk on the test run.

Thanks for the follow up. Any more comments appreciated. Regards.
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