Planing Trimarans

You're continuing to embarrass everyone with your gaucheness and ignorance Cav, but you seem totally oblivious to it. Perhaps it's time for you to go for a walk in the Pacific Northwest woods; I'm sure they are very impressive ... and it will take your mind off the quagmire you've created for yourself.

 

it was a 15hp right at the back. with two people sitting on the bow the bow was still miles clear of the water. The buccanner has a lot of rocker so I dont think it would plane like a farrier.

My new boat however is nice and flat like a Farrier. Im thinking about putting a 30hp on it for cruisng. I think it would do 20 knots easy, especially with some trim tabs. (with the floats still attached)

Im not sure compairing a 9m racer cruiser farrier to 100ft maxi tri is very relevant?

 

They are different purpose designs for sure. I'm don't know how big your current boat is but the horse power required for higher speeds jumps tremendously. The Macgregor monohull has to run a pretty big engine to go over 20 knots.

 

Planing Tri?

Why yes,as a matter of fact:

Frank Bethwaites HSP

Click on the image and then again on the subsequent image for max size:

 

Looks to me as if its just dug its arse in and is in displacement mode.

 

Yeah, thats it Gary!

 

into the lions den

I never sailed the HSP but CT249 did. He tested it for a mag.

I talked to Frank about borrowing the boat when I sailed Tasars. It just never happened.

The diff between the HSP and normal tris is that the HSP doesn't use the floats for buoyant stability to leeward. It is really a big skiff with everything reduced and little floats for help tacking and in lulls.

I remember seeing the thing a fair bit and it looked like it was planing to me (lots of spray) but I have no real definition of planing anyway. To me the 16ft skiff doesn't plane, at least it never felt like it to me. The hull on the HSP was long and thin so it was not a good planing shape. (I feel that the Laser, Cherub and raceboards plane)

As to how this helps the Farrier cause - it doesn't really. The HSP is not like a normal trimaran. It is really a trimmed skiff with floaties. Julian Bethwaite (the helm in the shot) is a skiff designer. The Farriers still get light because they load up a float whereas the HSP only gets light because of dynamic lift. I thought the HSP main hull was most like a D2 raceboard in shape. I don't know if these really plane either! Then you have the scale effect where the HSP has an incredible power to weight ratio compared to a Farrier so it may plane but the ten times heavier Farrier with much less than ten times the power may not even when built to the same design. (witness the fake planing of the 40ft stinkboat cruisers - they are just too heavy for the power plant - thats the scale effect - you can't plane a normal non race power boat over 40ft)

It would be a brave person to do this to a Farrier hull - put long beams on with stubby floats and use the crew to keep it upright. If it planes then it planes but it would be very hard to do.

cheers

Phil

 

Planing skiffs are a bit different to most tris

What he said....

A very sensible contribution IMHO Phil.

The HSP is a very different type of trimaran than the ones we are discussing in general - a bit like the Tri-Fly I mentioned in my post a few pages back.

I really don't see this just before it passes the mono - the boat does lift (but it could be from a wave, or it could be similar to the sequence discussed below - it is hard to be sure) and there is really no reference point to see clearly any acceleration from just before that point. The best example of what we are discussing to me is the sequence a bit further on with Alcatraz in the background where the main hull gets out of the water to about a third or more of its length (refer pic). Now this may be the main hull planing to some extent, but without doubt it is getting some lift from the leeward ama digging in very deep which you can see as you run the film on a bit further (refer pic). How can the boat as a whole be planing with the ama digging in so much.

Is it fast? Damn tootin!
Is it fun? You bet!
Can it give the most hardened lead miner that grin one recognises as the "multi-hull moment"? It did for me.
Is it planing? Well I don't know - but I dont think so.

Earlier there is a sequence with the leeward hull toward the camera and it comes through a wave and then the boat starts to lift but look how far down in the water the ama goes. (refer pic).

Finally look at the front on shot (refer pic). The main hull is so thin when viewed front on. I am no designer but I find it hard to believe that hull shape would plane without assisting lift from the ama displacing to leeward.

It pains me to contradict Ian Farrier, the designer of the best boats I have ever sailed or owned but to me the boat in its entirety does not fit the definition of planing. I am sure my comments make no difference whatsoever - but that is OK. When I get enough money together I will be buying one of his designs again. What this exercise has done has reminded me how much I love Farrier tris whether they can be really said to "plane" or not.

Cheers,
Andrew

 

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1) ...but it is a planing tri?

2) I don't think you contradict Farrier at all: he has never , anywhere claimed the ama's plane!! In fact, that's the crux of the whole discussion: can a main hull plane even though part of its weight is supported by the non-planing ama?
Maybe it's ok to describe a planing trimaran as such even though it's amas don't/weren't designed to plane: Frank Bethwaite on p 186 of High Performance Sailing says this about one of his HSP's: "Mk XII was a slender planing trimaran with a bow, a stern hung rudder, and tiny flying boat style tip floats for static stability only."

 

Is it a planing tri?

Is it a planing tri? Probably.

But so would be Chris' suggested Laser with some amas tacked on from a page or 2 back - that doesn't really make it a good tri-maran designed to get the maximum out of a rig.

You said that the Weta and F27 plane. My view remains (Ian Farrier's comments not withstanding) that the when the main hull lifts on those boats it is mostly from lift from the leeward ama digging in and forming the "hinge" for the boat to rotate around. There could well be, probably is, some element of dynamic lift but it seems to me the lift provided from the ama digging in will be far more dominant (force diagrams again).

Regarding planing amas - This from another thread....http://www.boatdesign.net/forums/sailboats/small-trimaran-ama-design-32966-2.html

Doug, what are you saying regarding planing amas here?

Cheers,
Andrew

 

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See the quote in the previous post for Bethwaites own description of the boat.
You say the HSP is not like a "normal trimaran" which raises some interesting questions.
Are the boats depicted in the pictures below monohull keelboats or are they trimarans-not "normal",of course?

Pix:
J. Bethwaites Pterodactyl
Sean Langmans Maxi Skiff
Trapwing Prototype

 

They look a bit like lead bellies to me......

BUT the proof is how do they sail, and how much advantage over a true leadbelly do their amas provide? Do they go faster because of the amas?

I notice all the pics are models or 3D graphics. Have any of these been built and sailed? Any pics?

 

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That the 4' ama would plane when the canoe was doing hull speed if it had a properly designed planing hull. But I am quick to point out that with the hull in question it is probably not a good idea to go with a planing ama.

 

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So if you were in charge of declaring whether these boats were monohulls or multihulls would you try(no pun intended) to come up with a percentage of ama immersion that would designate the boat as a trimaran? Or would you go with the fact that each boat is designed to be self-righting and has a ballast keel?
None of these boats or anything like them has sailed yet-to my knowledge.
(except as an rc model for a similar boat)
Is there a question in your mind as to whether these boats would even sail?
I can tell you that the amas in each case fit Phils and Bethwaites descriptions exactly-they are only for static stability and emergency back-up.
The boats are NOT sailed "on" the 'amas'. They go faster because of the moving ballast supported at their widest point....not because of 'amas'.

 

I am not saying anything in particular.

Just asking about the boats.

It was ballast keel that caught my eye.

You pose an interesting point - if built would they race against monos or multis - and how would they go against either?