Boxy Fisher Catamaran idea

Fanie
The folding arrangement looks smart.

I am cautious about the engineering detail of the clevis and pin arrangement you have drawn regarding the torque loading in the beams.

I am not current with the overall configuration of your cat these days so do not know what role the beams play in the structure. The torque loading is usually the hardest to seal with. The extreme loading condition for beam torque is when the bow of one hull and the stern of the other other supporting the entire weight. When your are beating to windward this could be a cyclic loading condition.

You have your model hulls. Make some model beams and stress them to failure. I think your clevis joints will be the weak spot if they are as drawn.

Rick W.

 

I'm trying to get hold of a structural expert here, but I got quite a shock this morning phoning for prices. A 100mm dia x 600mm 'pin' in SS is charged almost R5000 for I will need only four... so I first have to find a way to make a pin like that for cheaper than the rest of the boat.

Wood floats, I can just see the wooden pegs pop out there when they submerge

There is going to be an elegant and strong enough way to make these beams.

 

One thing that is irritating is the amount of hull space taken up if the beams fold into the hulls like they do. The hulls are already narrow enough.

I will see if it is possible to have the beams on top of the hulls in such a way that it would be an enhancement for the cabin one way or another.

Be a first to have a bridgedeck clearance of 1600mm though

Which gives me an idea - you can sleep in a hamoc under the deck...

 

I actually thought of something else as well earlier today.

In our case we are always going out with two or more vehicles, and it may be so for a lot of other guys as well.

That being the case, it may well be possible to have the catamaran split over the cabin centre, half a catamaran on the one trailer and the other half on the other trailer. To launch you move them together, tilt the two hulls towards one another and join the two halves.

This will be an instant cat with cabin, to assemble could take a few minutes only. The only restriction is the BOA which is limited by the trailing regulations, here it would be 2.5m, and a boat width of 5m. Should be good for up to 8m or even a 9m cat.

 

Something to this effect,

Red as you trailer it left and right.

Blue when you tilted them towards one another to be joined.

Since most of the structure is in place already, it should be sufficient to stick a couple of allu beams through the split for added structure.

Most difficult would be to pull the two trailers beside one another

Using a simple joining bracket between trailers, you can launch with one vehicle. Taking the boat out same thing. One vehicle takes both trailers out, with the boat in place, disconnect the 2 halves now leaning against each other, hook the tilt winch on each hull and pull them in place.

Remove the join bracket, and both vehicles can take off with their trailer.

A simple canvas cover could close the cabin's open ends.

 

I have been looking for a less rediculous price solution for the hinge's shafts, and engineering plastics came to mind. One problem one could have is the amount of water some plastics absorb, which may cause the hinge to want to freeze and huge pressures may build up in the hinge.

One of my favourite materials is HDPE, used it for some things to make before, however in this case it just may be the right thing.


HDPE tensile strength is 40n/mm^2 (Maizey plastics)

100mm dia ~ 314kN or 31 ton, cost ~ R 700 for 600mm and I can breath again (vs R 4600 for SS)
Not as strong as SS, but won't this be strong enough ?

70mm dia ~ 154kN or 15.4 ton

50mm dia ~ 78kN or 7.8 ton

Couple of other advantages as well.

HDPE can absorb only 0.25% water.

HDPE does not shatter under high impact, most other engineering plastics do.

Self lubricating, and won't wear the fiberglass out either

Lighter in weight even as a solid, than SS

Less noisier

UV resistant. I have some PE in the sun here for 8 years, it still looks brand new.

A friend has a press with a guage on it, couple of simple experiments would quickly indicate how accurate the calculations are.

So it seems from a financial point of view it may well be worth it to overdesign the hinges a bit, as well as gain on a few other advantages.

Maybe I will sleep tonight

 

The situations some 'friends' won't put you in

I went to visit a friend in hospital this afternoon, heart attack and in for an operation tomorrow.

Shame, while there he said if he doesn't make it I can have his fishing rods and reels.

I said come out and you can give them to me yourself...

He said no, if he makes it, he may go fishing again

Now what must I think eh

(We're that old already ! ? ?)

 

I think it may be time for a beer or three followed by a beer induced sleep, wake refreshed and think through some of the issues again?

 

Hi Mas,

Actually, I feel like I need more than a beer and a couple of blo... more beer.

I haven't been on the water for the last 6 months, really very grumpy and P O. Bad extraction symptoms

As if that's not enough, been working our butts off here lately, but gained bugger all with the R up to **** and everything going up 30 to 50%

4 5 c

 

Similar issues this side but I guess not quite so severe both in monetary and war like? - - - terms.... not good news to your north (Congo) I hope the disease does not spread... Take care.

 

Hi Rick,

I'm sorry, I'm not ignoring you. As usual your observations is spot on.

I would like to gain enough information first before deciding what and how many I will be getting.

The drawings will probably change some more. I still have to get hold of someone that can calculate the fiberglass strength on the clevis. It seems the multiple clevisis instead of the 2 per side would favour the pin strength.

More forces I will have to consider it what a sail will bring to the party on a beam reach... that and the possible water side force on the hull below may make for some rolling moment on the hull.

 

Fanie
I would consider doing the whole hinge arrangement in stainless and then connect it to fibreglass tubular beams. Make a flange on the stainless plate that you bolt and epoxy the tube to. The clevis is formed from flat bar welded to each face plate. The hinges could be just bolts with nylock nuts that can be nipped up once you get everthing in place. Need to consider the forces but a 20mm bolt at the four corners of a 300mm square plate would take substantial torque.

Rick W

 

I actually considered a cap made from 6mm SS that would fit snug over the beam, and multiple 10mm ears protruding as the clevesis. This can be made easily and would be quite strong too. Just one disadvantage, it adds quite a bit of weight. I will go this route as a last resort.

I had a brief chat with the structural designer this afternoon about the beam. The problem is the sharp turn the fiberglass makes from the beam to the clevis. Fiberglass doesn't like sharp turn like that and he said that is where the weak point(s) are.

I actually have another idea, but have to draw it first.

Back to the board

 

Only in SA

My anchors, or rather one and a half anchors got delivered today. No, the ***** that did the laser cutting didn't understand what two sets are. Cannot count to three pieces. Even the driver that delivered the stuff managed to count that high.

They will send the other two pieces.

Tacked the one anchor together this afternoon and had a brief 'play' with it. Bloody heavy, so I didn't play with it for long

I wasn't going to pull it over the paving for fear it would set and I'd rip a strip of the paving out there

I can't test it in the pool either, the wife would kill me

Once I have all the pieces together , I'll weld them up properly, do a bit of cosmetic grinding on them and send the anchors with their chain in for hot dip galvanizing.

 

There are going to be 2 anchors, one for each hull, 10m x 10mm chain for each. If you want to see the chain I can upload a picture of that too

The anchors cost me R 650 each, the chains were roughly the same. With the hot dip galvanizing it is going to be around R 1400 per anchor with chain.
Doing the welding myself, so not counting that as an expense.

At least the boat I don't have, have a handbrake