22 - 24 trimaran

[Gary Baigent]

In crappy black weather, leave them both down, in fact leave them down all the time - it is only in very light conditions when the fractional drag from the flying windward dagger might trouble the most paranoid of competitive sailors, that the windward one could be lifted so the tip flies clear.
I'm pretty sure Groupama 3's huge curved foils are not lifted by some jokers toddling out there up to windward and hoisting them by hand. That is not the reason they got into trouble. I thought it was from heavy breaking waves smashing against the float - not a lot you can do about that in such conditions, a trimaran/multihull configuration problem.

 

[bruceb]

black nights- timid crew

I will probably spend the dark nights on someone else's bigger boat, but it is nice to know that disaster shouldn't strike because the boards are left down. I don't think I want to go out there in a blow. I notice in most of the photos that the crossbeams don't have much "flex". Mine are down from the joint out a couple of degrees at least- particularly the forward one. It puts the floats noticeably bow down but the boat doesn't heel as much. I just used the settings that the previous owner had used. (my forward water stays have a turnbuckle) Any thoughts?

 

[Gary Baigent]

B24 floats bow down

Actually Miranda carries the floats bow down a bit too - but if you fit foils that is no worry as they rectify the nose down attitude. You'll hear armchair admirals say that if you nose down a steep wave, the foils will provide negative lift and bury you even further to the point of an end over - I've never experienced this, in fact the foils keep the overpowered float up and reduce the expert's capsize fantasy. Not saying it couldn't happen if you drop out of a huge, tumbling wave front surf - but in such conditions you're in deep pooh anyway, foils or no foils.

 

[bruceb]

board angle

There is a wave out there bigger than any boat- I guess I will take my chances. I am concerned about my ability to get the board trunk installed at the right angle- I am not sure what part of the float to use as a base line. I have installed boards and keels on center line but this is different.

 

[bruceb]

board questions

Oldsailor, were your boards vertical or angled in your tri? I have never sailed on a boat with angled boards, but the lift they give seems to change the whole dynamics. Since I am on the other end of the world, news takes awhile to get here- has anything been determined as to why Groupama broke up? I know the bow folded but not much else.

 

[Gary Baigent]

B24 angled foil fitting

Fitting foils is no big deal Bruce - although the directions here make it sound more complicated that what it is. Run and stake tight lines, one from the main hull bow to middle of stern, another from float bow to stern (you'll have to use a plumb bob to get the positions on ground). then measure at right angles from hull to float lines at the position of your foils and there you have the measuring points. You have to cut slightly wider holes in your floats for the foils and their (strongly constructed) cases, slot them in dropping the foil to touch ground (it will be a metre or so on the ground towards main hull) measure on the ground the leading and trailing foil edge positions and check and recheck alignment, then when you are satisfied, epoxy the cases in. By the way, on angled towards main hull foils, the higher curved faces of the foils are positioned facing TOWARDS the main hull, the flatter surfaced areas TOWARDS the float, this is a basic that some people are unsure about, you don't want to mount them upside down.
Although Miranda has her foils set at zero angle of attack, I would suggest 2 degrees toe in (you might as well make full use of the lift and less drag of asymmetrical foils) then you will really climb to windward. If you look at the jpegs of Miranda you'll see that the foils exit slightly inward of the float keelson, means you don't have to cut timber, just ply. Any greater angle you set the foils through floats will make this position higher, doesn't matter, although the closer you are to the float keel the better, less chance of aeration. Remember the greater angle, the less canterlever support area there is for the foil cases - and also the more difficult it is when sailing to lean out and physically fit or lift foils - Miranda's setup is a good compromise.
.

 

[RHP]

Wayne, I always favour buying secondhand to save money and get on the water without delay. Maybe I'm poor or lazy. Maybe both.

I cant work out whether you said you want a lightweight flyer or whether the thread just progressed that way however I have always like the Telstar 26 which are freely available around the UK from rebuild candidates (I know 2 worn out ones that need complete refurbishment) through to ready refurbed and all between.

Nice deep cockpit, amazing interior considering its size, trailerable and cheap.

What more could you want?

 

[oldsailor7]

Oldsailor, were your boards vertical or angled in your tri? I have never sailed on a boat with angled boards, but the lift they give seems to change the whole dynamics. Since I am on the other end of the world, news takes awhile to get here- has anything been determined as to why Groupama broke up? I know the bow folded but not much else.

Last question first.

Groupama 3 broke its forward crossbeam right at he point where it enters the deck of the port outrigger.
Final analysis was that the skin of the outrigger failed in fatigue due to the continuous stress reversals between the side loadings on the end of the crossarm and the torsional loadings provided by the lifting daggerboard, which was situated right behind the crossarm junction.

It is impossible to calculate these structural forces because the sea doesn't go by the book.

Lock Crowther told me that to be safe, after the loss of his first successful ocean racing trimaran, he took his initial stress calculations and then increased them by a factor of 6, to be on the safe side.

This can be over done of course, which will result in a structure which is too heavy.

The Buccaneer 24 was Locks most successful design in terms of numbers of plans sold. He set out to design the simplest, yet best performing small CRUISING trimaran, based on the idea of three sheets of plywood butted end to end. The result was a pleasing looking boat which could be amateur built very quickly, in a small space, at minimum cost.

I am not one for "guilding the lilly". If I were to build a B24 again I would change nothing except extending the bows of the floats to be level with the mainhull bow, the underslung rudder option, and a more modern rig. with prodder and furlers on the forward stays.
On further thinking I would build the cabin with the MK2 cabin length, and the Mk1 cabin width in order to get the narrower sheeting angles so essential to good windward performance. I would also increase the aspect ratio of the centreboard with a rectangular planform and area of 2% of the projected sailplan.

AND

I would paint it April Yellow. LOL.!!!

 

[bruceb]

final choices

RHP, I think I am responsible for diverting the thread- as a former boat dealer I agree on buying used if at all possible. Far better value and you are sailing years quicker. Gary, I think you have answered all my questions, thanks! I will start measuring next week. Oldsailor, I didn't know there are two versions. The plan set (151) my boat was built from dates to about 1974, the inboard rudder is not shown. The cabin was removed from my boat- I have a 9' open cockpit, great for racing in the summer, but I will probably put a cabin back on some time in the future. Do your plans show both versions? I am not quite sure how I can fit the cabin and still be able to drop my mast easily, it sits on a ball on the cross beam. What is a "prodder"? I have a taller rotating mast, roller furling jibs and assymetric spinnakers, just what every "cruising" boat needs.

 

[oldsailor7]

BRUCE.
If you put the cabin back on in accordance with the plans, the mast sits on top of the cabin , just as you have it now. It is supported by a 4 3/4" x 2 3/4" compression strut in the cabin. You can leave the mast as it is and lengthen the shroud wires, or shorten the mast to suit.

A prodder is just a newfangled name for a bowsprit. LOL.!

If anyone would like a study plan of the B24 I can supply one gratis if you just send me your postal address.

PM me if interested.

 

[bruceb]

Changes

Ha! I learned something new- I have a retractable prodder. Carbonfiber too. I got out the plans and looked at the strut. I think something like that will work with a little rework. There is a lot of forward horizontal load when I am stepping the mast that I will have to account for. I have to do something new, my white boat looks so dull after seeing the pictures of Miranda.

 

[waynemarlow]

Wayne, I always favour buying secondhand to save money and get on the water without delay. Maybe I'm poor or lazy. Maybe both.

I cant work out whether you said you want a lightweight flyer or whether the thread just progressed that way however I have always like the Telstar 26 which are freely available around the UK from rebuild candidates (I know 2 worn out ones that need complete refurbishment) through to ready refurbed and all between.

I certainly do agree on the second hand route but so far have found nothing that really jingles my bells. I probably would say that racing and lightweight would be higher priorities than cruising, which sort of eliminates the Telstar and somewhat the Buccaneer. The ST7 is very nice if it had a small cabin big enough for overnight stays, the F28 is very very nice but is expensive to build and now getting a little dated in looks.

 

[bruceb]

Gary, I have plotted the foil shapes, and they look sort of fat? Sort of like the wing profile on my old piper airplane- lots of lift, but a lot of drag when you were trying to go fast. I am just learning to use xfoil and I don't have any experience with assymmetric boat foils. Maybe they are correct. The shape of the current offshore racing multi's foils seems to be very well kept secrets. Any thoughts?

 

[Gary Baigent]

the dreaded foil word

If you look at the earlier posted jpeg of the asymmetric foil, you’ll that is a 12 % thickness to chord ratio - in my opinion not a bad compromise foil for both high and low speed performance. Also at that thickness you can grind out two shallow scoops a couple of feet long both sides of the thickest section in the hard spot area (where the foils exit their cases) and fill the scoops with layers of uni directional carbon. Remember most of your boat’s weight will be resting/leaning on that small area when you are foiling hard in waves and a fresh wind. You need some meat in there. So far, although my foils are low technology: strip planked wood, carbon reinforcing, sheathed in box weave glass/bog for fairing, I haven’t broken any from sailing loads. This is not to say I haven’t wrecked a couple (and cases) from slamming into sunken reefs at high speed.
If you prefer to go to symmetric foils, keep them at or near 12% too. But asymmetric shapes are superior. However there is another simple-to-construct shape and that is ogival foils: an arc of a circle shape in the top section and completely flat underneath, with the leading and trailing edges being very sharp points. The Grogono brothers used such foils on their famous Icarus/Tornado cats – and they worked extremely well. They were also very fine, (at a guess 6-7%) and built in metal with a solid beam inside at the middle and thickest section point. You could easily built them in wood (but a bit thicker) with carbon/glass etc.

 

[bruceb]

A test

Gary, I think I am going to make two different boards and see which I like best. Maybe one 10-12% asymmetric and the other like the tornado board. I can then make a mold of the better board. Thanks for the advice. Sailing in the eastern US, ground contact is a matter of when, not if. I really like getting the dagger out of the main hull, damaging the float is a lot less of a disaster. I have dingy airbags stuffed everywhere for a back up. I am making my cases "adaptable" with removable shim strips, it makes the boards easier to slide also. This should be interesting, I will report back in about March with some pics and results. Bruce