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Pahi31 beam attachment

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Anonymous (not verified)
Pahi31 beam attachment
Does anyone have any ideas for doing away with the bolt in the center of the beam pocket and just use lashings with some other method to keep the beams from moving sideways? Thanks, Frank
Anonymous (not verified)
Re: Pahi31 beam attachment
That doesn't sound like a good idea to me. Why give up stability, while keeping the flexibility? I'm about to change the rear beam, as the old one has gotten too soft for the motor. Can anyone tell me if a massive straight beam, reinforced with fibreglass and epoxy, is any worse than the laminated curved beam, as in the plans? I will also put a fibreglass tube connecting the motor support to the second beam from the rear, so the propulsion doens't just lie on one beam and those two bolts.
Anonymous (not verified)
Re: Pahi31 beam attachment
Nollaig Shona [happy Christmas] as we say here in Galway bay. I have made a new set of xbeams to fit without central bolts.I wo'nt be assembling and launching until early summer, I will try to post photos then which will probably explain things better than my Galway bay PAHI31 post. As for a straight beam I had one for a while. I made it as a temp. replacement for a soft beam which was not seaworthy. I made it as a girder shape with top and bottom approx. 2.5" to match old beam with 4 x 1.5" central piece. It was also packed out solid in way of the lashings and bolt. It worked fine but was way too ugly to live with. My new beams are girder shaped with straight bottom edge and top curved to match the designed curve of the origional. I used a heavy ply web (the vertical central part). This made them easy to build and they look fine. They are solid where the lashings land.The top and bottom are laminated. Unfortunately I have'nt fitted them yet but I really expect they will be fine. Do'nt forget if you eliminate the bolt the new pressure-point will be where the beams bear on the ends of the troughs and this will have to be beefed up. None of this is revolutionary- after all every Classic, Tiki and Ethnic builder has already done this !!! The beams and lashings on PAHI's are under a heavy strain due to having a very short lever-arm between the lashing position and the beam bolt.With a TIKI style arrangement this arm is doubled so the pressure on the lashings and beams is halved. My lashings are impossible to keep tight in a seaway and I'm no perfectionist. Taking the sidestays to the outside of the hull while standing the mast beam on the inner side of the hull does nothing to help if you think about it.
Anonymous (not verified)
Re: Pahi31 beam attachment
Hi Seamus, What method do you plan to use to resist the sideways movement of the beams? I too am replacing my beams on my 31 and JWD sent me plans of a laminated I-beam style, also with plywood center web, similar to the Tiki style but with curved tops to match the original Pahi shape. JWD's plans show reinforcing those pressure points on inner and outer edges of the trough by a small triangle plywood gusset adding support for the one edge of the trough not supported by the full bulkhead. JWD plans resist the sideways movement with a center bolt/pin but the hole in the beam is oblong up and down, which allows freedom for the beam to move up and down but not sideways. I believe this is the method used in the larger Tiki's. The only advantage to this method I see is that if the lashings failed there would be some resistance for the beam not to completely separate from the boat, but I think this is so unlikely to happen. Although this method is proven to be satisfactory on the big Tiki's it seems like an awful lot of extra work creating waterproof bolt holes through the trough walls into the cabin. I was wondering if one couldn't just add a couple vertical stainless dowel pins between the support pads, on the outer edges of the troughs, and the underside of the beam at the lashing points. That would solve the sideways movement and also align the beam in the trough without side shims. What opinions does anyone have of this idea? I hope to relauch this spring (2011) and as soon as weather allows I'm ready to fit the new beams. I'm still debating that beam sideways movement issue but leaning towards the dowel pins as it would be very little work and would also eliminate any need for fore/aft shims in the troughs as well as no holes into the cabin. Happy New Year, Frank Pahi31 "Mikyla"
Anonymous (not verified)
Re: Pahi31 beam attachment
Seamus, are you using "frapping" around the lashings? I pull the lashing as tight as humanly possible, and then use the frapping line to really tighten the grip of the lashing line. [quote="seamus"]Nollaig Shona [happy Christmas] as we say here in Galway bay. The beams and lashings on PAHI's are under a heavy strain due to having a very short lever-arm between the lashing position and the beam bolt.With a TIKI style arrangement this arm is doubled so the pressure on the lashings and beams is halved. My lashings are impossible to keep tight in a seaway and I'm no perfectionist. [/quote]
Anonymous (not verified)
Re: Pahi31 beam attachment
There are two aspects to reinforcing the troughs. Mostly structures distort before they fail so you must preserve the shape the ply triangles will do this. You also have the crushing load. I will be strengthening the cabin sides inside between the bottom of the trough and the inwhale [cabinside/hull joint] by infilling between the various stringers with short lengths of timber to make it all flush and solid and fitting a ply facing over all. Alternatively you could fit a doubling piece outside between the gunwhale and trough with the pad coming out over the top of it for support but would it be ugly?? I will fit pads at the ends of the troughs with a drain to prevent filling the trough. As regards sideways movement I plan to fit blocks to the base of the beams where they exit the trough. The bow and stern beams are still bolted so the hulls are held in position during assembly and these blocks will be fitted after assembly which is probably the only way to position them exactly. The blocks will be tapered off for aesthetic reasons and about 2" thick unless someone out there knows better?? Lashing a PAHI is quite an art. On most boats the beams rest on pads. You tighten down to the pad as tight as possible with frapping etc. and the job is done. Pahi beams have no pads. Instead they balance on a central bolt to make a perfect see-saw. Each lashing affects its partner. You must embark on a tour of the boat working the lashings in turns much like a mechanic with his torque-wrench fitting a head on an engine-block.As you travel up and down the boat you cause small changes in trim which undo the good job you did on that last set of lashings and on and on in an endless loop.....since no beam has a fixed position each tight lashing must create a slack one somewhere else.....eventually you resign yourself to sailing two hulls that seem to follow one another through the water largely through force of habit.... To compound this the downward pressure of the maststep is transferred via a partial beam to the inner edge of the hull while the side stay goes to the outer edge. If you calculate the force-couple [twisting] transferred at 30% load [approx. 500 lb each for maststep and stay] you get a couple of 2000 ft/lb [one ton] which must be resisted by the beam lashings..... The tuning of a banjo is an exact science by comparison I hope this does not sound very negative [or my earlier posts] this is not my intention. It is perhaps difficult to offer improvements without appearing to be critical. Happy sailing roll on the summer!!!!!!!!!
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