hull and speed

[niels]

Everybody is always talking about fast hulls and slow hulls.
But when i'm on plane and trimmed out(WOT) there is only 1 meter(or less) hull left in the water.
So if you have two hulls with the same weight, length and weight distribution(and engine offcourse), how important can the shape of the hull be???
I'm very curious.
Can anyone tell me?
Greetings Niels.

[Seb]

The hull shape and thus hydrodynamics are VERY important in determining the top speed of a RIB.

Think about it; if you had two cars with the same engine and weight in them but one was a sleek sports model and one was a bloated 4x4, which would be faster?

Same type of idea. The design which is likely to cut its way through the opposing matter the best, be it air or water, will be the fastest.

Cheers

SEB

[niels]

But the hull nearly doesn't touch the water in both cases at wot.
the last meter in the water has almost the same hullshape.(both deep v)
Is it maybe only the wind resistance then?

[simmons0]

A 'slow' hull most likely won't lift out of the water in the same way as your revenger does

It might be on the plane but still have more hull in the water than a different hull shape.

[Swifty]

Another very important factor is how deep the Vee. In flat calm water a deep Vee hull will sit lower in the water for the same weight/speed than a shallow Vee. Hense if its lower theres more wetted surface which causes drag. So the shallow vee will be faster.
This is all fine until the water is not smooth, then the shallow vee will bounce around so hard it will have to slow to maintain control, Whereas the deep vee will be better able to cut through the wave.
Some top race boats have very deep vee's forward and rapidly flatten out at the stern to try and get the best of both worlds. I believe this is called dead rise??

As an example we paced an avon SR4 with 30hp and a SR5.45 with a 90hp. The SR4 won closely followed by the SR5.45. but when the wind blew up the SR5.45 just kept going whereas the other couldn't maintain control and had to back off.

In the overall equation fast hulls are rarely good in rough water. Its all a compromise between speed, stability and how well it will ride out a chop.

[Brambles]

Originally Posted by niels

But the hull nearly doesn't touch the water in both cases at wot.

Yeah, know what you mean.....

[gavin]

Hysucat

[Jonny Fuller]

Originally Posted by Swifty

Some top race boats have very deep vee's forward and rapidly flatten out at the stern to try and get the best of both worlds. I believe this is called dead rise??

It's actualy quite rare for this hull form in out and out racing.

The term 'Deadrise' when used as a generalisation, is refering to the depth of the 'V', usualy quoted 'at the transom'.

'Constant deadrise' refers to a hull with a deadrise that is substantialy the same at the transom as it is in the forward section. (by far the most common form for all out racing)

A 'Warped Deadrise' refers to form you described with a deeper 'V' in the forward sections, than at the transom. This form gives a very soft and 'pitch stable' ride.

[Swifty]

Jonny, many thanks for clarifying that.

That picture from brambles, if you look at the guy in the white t shirt, what was he trying to say?
Should we start a new thread "caption competition"

OK so landing gear hasn't come down.... brace brace brace
or
I told you there was a rattle from the dash when it does this.

[niels]

greetings
niels

[jwalker]

It surprises me how these ribs get there bows so high out of the water when there are almost no waves. In niels pic it looks as though the wave height is little more than about 300mm. Do your boats really handle that badly or are you just playing?

[Mr-d]

Erk, how can you see where you are heading like that?! Do you have a camera on the bow or something?

Look's like someone needs to play with the trim!!

[niels]

we are just playing off course
only hitting the trottle a little firmly.
the bow goes as high as I want her to go.
the boat handels like a dream. 65 knots no problem.
I love this monster.
again greetings from a wet and grey holland.
can't wait till summer. and I don't think I do.

[niels]

on our way to ribex 2004.

[Mr-d]

Hey Niels, whereabouts is hoorn? I've heard of it but i cant combine it with water somehow... braindead i guess... is it in Friesland? or where?

I wish you good luck in the summer with all the Germans in their big fat Motorboats! One way to make them scared is probably the manouvre of fast acceleration as the pics show! Ahhh, i can just imagine it "Verdammte Ar****ch! " hehe

[niels]

[osprey__viper]

......... is one of the nicest places I have visited in Holland . Went there on me dads boat (moonraker 36) in 1990. Two great weeks cruising the iselmere (?) with a north sea crossing at each end.

Only a couple of meters deep and some of the biggest waves you can ever wish to meet!!!!!!!!!!!!!.

Martin

[Mr-d]

Ive never been to hoorn, but have done some sailing back in the mid 90's around the Afsluitdijk and East side of the ijsselmeer and i have sailed up to 3 of the islands with my daddy....

It was kindoff an holiday.. but sailing is to slow for me.. everything takes to long, is to quiet and you cant really get anywhere instantly without to much hassle of navigating difficult areas (unlike a RIB!)

[niels]

[Alan]

I've been sailing in that area too, as a kid. We had a week from Monickendam (sp) and called into Hoorn. Nice place.