Converting a beach cat rig for cruising

Discussion in 'Multihulls' started by rayaldridge, Jun 24, 2011.

  1. rayaldridge
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    rayaldridge Senior Member

    The rig is set up for it, but I can assure you there will be no trapezing. I'm planning to use those wires to keep the mast in line while being raised.

    I'm wondering if running wire to the masthead will help keep the mast in column. My central spine, which carries the mast loads, will also be ideal to carry a prodder. I'm going to keep my eyes peeled for a used drifter in about the right size.

    I just went out to the shed and found my old swaging tool, so I can do it.
     
  2. AsterixDeGaul
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    AsterixDeGaul Junior Member

    ;) I had a feeling you were thinking of it along these lines ... Let's take your example, and now figure out the loads needed to fly a hull ;) You can see what happens. Wider = more heeling resistance.

    Now, I know that one might say "Well, I don't plan to fly a hull on my pocket cruiser", but ...
    As I mentionned, A N5.2 will fly a hull in 8knts, which kinda gives you an idea of the maximum loading the rig will experience .. Not much.

    If you're anything like a normal sailor, You will be loading up the rig, sheeted in tight long passed 8knts of wind since your boat will be wider and perhaps heavier.

    Anyway, I'm sure it will work out fine.

    3/16"(1x19) is quite strong.

    BTW, I like your Slider, very pretty.

    Can I ask what boat you are putting the N5.2 rig on ? Have you built a new boat ??
     
  3. cavalier mk2
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    cavalier mk2 Senior Member

    If you run a wire to the masthead you will need some kind of running backstay for it. Or set up the rig as a masthead with a primary staysail with stays/running backs to its mast location. I ran masthead running backs on my fractional rigged uldb for the asymmetric chute and it worked great. A wire luff light genoa can make a good cheap screacher if you don't need the masthead forestay, keep the running backs though so you don't have to watch the upper mast bend while flying it.
     
  4. rayaldridge
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    rayaldridge Senior Member

    It's true that wider means more heeling resistance, but not more compression.

    Thanks. I'm building a new boat:

    [​IMG]

    Truthfully, the boat started out as an answer to Jim Brown's very clever new line of trailerable tris. I have a personal preference for cats as cruisers. But they are, no doubt about it, harder to make trailerable. I have a scheme that involves the boat folding at armpits and along a central spine. I don't know if it will work yet, but it seems plausible on paper, and using models. The hope is to have a boat that can be folded with the rig up, so it can use a narrow slip, since that's what's available to me.

    Running backstays: cavalier, do you think runners will be necessary? I was hoping that using a drifter in light air could be handled by upper shrouds to the same chainplates as the lowers.
     
  5. cavalier mk2
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    cavalier mk2 Senior Member

    That would work. Less to forget also. I'd try putting the chain plate even with the back edge of the cabin for a better angle, your main should still ease way out but if you draw the apparent wind forward it won't get all the way out!
     
  6. AsterixDeGaul
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    AsterixDeGaul Junior Member

    Well, truth be told, "column" loading will be the same regardless of BOA(roughly the weight of the boat) providing chainplates are set on the outside of the hull in all cases. The math is simple enough to show this. My point is, ALL other loads on the mast will be increased, Column loading is minimal and not the problem.

    Just a word for thought... When we run a chute on beach cats, we generaly have the main not far off centered on the traveller and sheeted prettty good. This keeps the mast tips from falling off too much due to chute loads. With this setup, we sail roughly 135degrees off the wind.
    BTW: Chute head block is often set near midpoint between main hound attachment point and mast head.
     
  7. cavalier mk2
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    cavalier mk2 Senior Member

    Sounds like additional stays or running backs could let you put the main where it is most efficient rather than using the mainsheet as the running back. It would let you run deeper.
     
  8. cavalier mk2
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    cavalier mk2 Senior Member

    In all fairness with a 8ft beam beachcat adding 2 guys on trapezes doesn't that = the righting moment and stress of at least 12feet of beam?
     
  9. AsterixDeGaul
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    AsterixDeGaul Junior Member

    You're right, but there i s always a little more to it.

    Ahmmm, I had to edit my previous post :(. The column loads on a multihull's mast at the point when "just starting to fly a hull" is = to the weight of the craft. As you pointed out, movable ballast like crew or water ballast will change things a bit, but I would think that Ray's 23 footer will have have 2 crew on the high side similar to 2 guys trapezing.(Hmmmm, one or two trapeze wires on a N5.2?) on a 5.2.

    What does change with increasing the beam is wire tensions which translates to mast bending loads. Hell, if I was ready to part with it, I would sell Ray my Supercat 20 rig and there wouldn't be any question of strength issues.

    * AND we haven't even entered the realm of dynamic loading. Let's not go there :p

    To Ray, sorry if I sound like a pest, I didn't mean to. I really do like your choice of boats and idea behind them. I'm sure everything will work out great.

    Funny thing is, I am contemplating going from a 16'BOA to 18' on a 28 foot cat I plan to build. 18 sounds kinda wide to me for that size but others are doing it successfully :/... Opinions ? (boat example : Firefly 850)
     
  10. Doug Lord
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    Doug Lord Flight Ready

    A Nacra 5.2 with two 170lb people on trapezes has a maximum righting moment of 3245 ft.lb.s, 1785 of which is due to the crew.
    Rays new boat, based on the specs on his site will have 11,400 ft lb of RM MAX* with crew/extra weight all in the center or equivalent to being in the center.
    In otherwords, 3.5 times what the NACRA rig is designed for.
    *MAX RM calculated with windward hull just above the surface. This needs to be looked at very carefully from a safety standpoint.
    =======================
    Correction:

    I forgot one crewman in the above calculation! Thanks to ADG for cathing this in post 28-I appreciate it.
    1) 2X 170=340; 340X 10.5(7.5 +3)=3570ft.lb. Hull- 365(boat weight) X 3.5(allowing forCB inboard)=1278
    Total 3570+ 1278=4848.
    --
    2) Rays boat: 6'(allowing CB inboard) X 1900(max displ.)=11,400ft.lb
    --
    3) 11,400/ 4848= 2.35 times Nacra Max RM. with two guys on trapezes.
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    Which ought to use up the safety margin. Commercial gear is designed around a 5-1 margin, I think rec gear is about 3-1. What did Newick's tremilino design get away with? It is a 23 ft tri that used Hobie 16 rig and the hulls for amas.How about coring the mast by inserting a web.
     
  12. bruceb
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    bruceb Senior Member

    wire size

    I think you should go up a wire size- 1/8" nicro pressed wires break quite regularly on beach cats, I watched a H-16 rig come down last year and I have a LOT of broken Hobie shrouds in my basement. Roll swages are stronger than nicro press, but not by enough. Prindle 19s and several other of the larger cats use 5/32 wire with swaged ends. My Buc was speced with 3/16, which would probably be overkill on your boat. For what ever it is worth, I have never seen a proper nicro press slip, the wire always fails right in the top of the press. I have read that the double presses were done to satisfy the attorneys, but there is a bit of practice necessary to do a nicro press correctly. There must be a good safety margin on most of the older beach cat masts, they never seemed to break from sailing loads but a lot of booms and wires did break. Dyneema might be the best answer. The 5.2 Nacras are one of the lightest of the older beach cats but I think their mast section was about the same as the others, and I think it will work fine for a basic rig, but if you are planing on adding masthead reachers and overlapping jibs, you will probably need a stronger mast. If and when it comes tumbling down, I have some H-18 sections that should survive:D. B
     
  13. AsterixDeGaul
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    AsterixDeGaul Junior Member

    Hi Doug.
    rough calcs : 2 x 170 x 11'(rough CofG for crew about fulcrum)=3740ft.lb for crew alone on a N5.2 ... Well, this is what I get anyway.

    I estimate the boat @ 1000ft.lb. (250 x 4) <- this one really is an "estimate"

    Was the N5.2 really set up with a double trap ? It's been a while since I sailed one.
     
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  14. AsterixDeGaul
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    AsterixDeGaul Junior Member

    Not sure where you get teh 5:1, The Lewmar blocks I bought not too long ago have written on them...

    SWL(Service working load) = X (pick a number :p)
    BL(Breaking load) = 2X ... This says 2:1 to me but I am not sure about this.
     

  15. Doug Lord
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    Doug Lord Flight Ready

    =========================
    You're 100% right-I was in a hurry and forgot one crew!
    I did 10.5 instead of 11 to allow for the CB of the lee hull being inboard a bit. And I allowed three feet from the side for the crew CG. Thanks for pointing that out. I'll correct the previous post.
     
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