Trailerable Multihulls

[JCD]

Hello to one and all,

Originally Posted by catsketcher

What is the polypropelene yarn next to the core? - I would steer clear of it if I were you. I think Dynel is polyprop and I wouldn't put glass over Dynel.

Olifin spun polypropylene is the strongest and most versatile of all the synthetic yarns and has a very high impact strength. The 4oz weave will provide bulk equivalent to 7.5oz and wets out readily. Dynel will be the outermost layer in all scantlings.

Originally Posted by catsketcher

As to Dynel - I used it on my small boat and didn't on the next one. It sucks up an awful amount of resin - very thirsty. It is not especially tenacious and according to my bottom of dinghy test doesn't stick that well when crazed. Good for sliding over rocks though but you will have faired your boat's bum so there will be some filler there.

I have looked into Dynel quite a bit, although I never used it. It is my understanding that it has excellent adhesion with poly or epoxy. Durability is also excellent. It is extremely durable and as a layer over glass it will reduce fracture crazing to the gel coat. It is very slippery so it reduces friction quite well. It also has a low weight to high tensile strength and can absorb loads up to 8x greater than glass whether working or impact. In fact, it will have reduced properties when used alone opposed to as an overlay therefore it contributes to the strength of glass underlay. It is easy to use, no fibers to cause irritation and resin to glass ratios are normal.

Originally Posted by catsketcher

Maybe you should increase the density of the filler ... Dunno but that is what is the first stage under the paint - anything tough will be hard to fair - maybe aluminum fleck in the clear resin over the filler. Anyone done this or similar?

This sounds like a great idea. Never did it so I wouldn’t know, but wouldn’t micro-balloons be a better solution for weight and ease of fairing?

Originally Posted by catsketcher

I wouldn't do the two layers inside. No real point as you can get very nice 600gm DB and biaxs. Laminating multi layers of glass has to be worth it or you will curse yourself during building. As for the outside laminate I would only double below waterline - use one layer above.

I guess that anyone would have a lot more sensibility about this than I. I don’t think that I can really point out a right/wrong or good/bad way for this to happen. I suppose bi and tri axial is always a choice, but I was trying to settle for the best property for the least cost. Two layers over 1 layer is always stronger if the weave is aligned to the loads so it is always worth it.

Originally Posted by catsketcher

Glassing over a fully cured glass layer is not especially easy - the knobbly surface needs prepping. If you sand too much you will take away strength of the initial laminate. Doing two or more laminates at the same time is tricky.

Agreed. But with proper resin/hardner ratios, there will be enough time to lay up all layers wet instead of waiting for a cure. It will take more prep time before the layup but the design is small enough so that it can be done.

Originally Posted by catsketcher

Secondary bonding considerations, ease of building and cost would have me recommending a single laminate with another only below the waterline (outside) for trailers and rocky beaches to have a slug at.

These construction issues are tough for me to solve because there are as many varied ways to do it as there are construction materials. Secondary bonding is not an option for the many reasons already pointed out. It is hoped that the extra prep time to get all layers laid up in one shot will exceed the labor that will be required with sanding and fairing the entire area to be readied for the next layer.

One layer is going to mean lots more print through and filling and fairing, as opposed to larger weaves and heavier glass closer to the core with smaller weaves and lighter glass outside. I suppose that the same required strength could be obtained with a suitable single layer, but I also think that the final labor and weight difference could be large due to all the fairing and filler.

Originally Posted by catsketcher

Also I would say your keel strip is way underdone. If going on rollers you will have huge pressure on the laminate above each roller. One layer of 440uni or DB will not be enough unless the rollers are very well adjusted and core is very high density. Check your rollers and hull shape to see if you will have a concentrated keel load.

Really? Okay. I will look at it again. Durakore density is not very high but I thought that all the traverse bulkheads from furniture etc., would reduce spans quite enough to provide solid waterline areas from a 5/8” core.

Originally Posted by Chris Ostlind

The graphite in the mix is a self-lubricating compound that wears away, marginally, with each encounter with a harder surface, much like the ends of a typical graphite pencil. The lubricity provides a slippery surface for the boat as it glides over the harder rocks and gravel.

Initially, I wanted to lay down 8 or so layers of copper-poxy on the water areas for superior anti-fouling properties to the design and then I thought, hey, the skipper can choose the option if he is in the water for significant periods instead of dry sailing. The graphite is the way to go for this design to keep her bottom easily serviced and allow her to be as slick as possible while on her bottom to further reduce drag associated from an already heavier design.

Originally Posted by tspeer

For example there was a Formula 40 catamaran that used to race in our area, and the standing joke was that he had to finish before the race started in order to save his time!

That’s funny. That's like saying he will never lose because he will never start.


I have questions that I hope some of the more learned and qualified heavies around here may be able to answer or opine on the rulings made through interpretations.

This is from German Lloyd:

“The FEA model must correctly reflect the geometry of the rig as specified in the sail plan.".

1. Does that mean that all EU governing bodies expect the mast to be designed according to an FEA result, or does it mean that they will just “analyze it” as such but will contribute little if anything by way of suggesting the mast geometry and scantlings? If it is, then which software would be acceptable to them for the study? It appears that they all like to provide ticklers such as safety factors for the mast components but steer clear of defining actual mast design criteria. Why is that?

2. The RM is to be calculated at 30 degrees. If a cats maximum righting moment is when the windward hull flies, what would be acceptable? ISO wants the calculation to be made at first reef which results in a reduced RM, so which is the reasonable to consider for offshore conditions:

a. Full RM as the hull clears the water.
b. Partial RM at 1st reef.
c. at 30 degrees, which results in a RM 13% smaller than zero heel.

Thanks again,
J

[Chris D. Brooks]

finally found a forum on trailering a multi-hull. I’m the newbie here so bare with me. I’ve raced tunnel hulls for several years and love the design. I’ve been looking to build a power cat but want one with enough room to sleep overnight, head, etc. The problem is I don’t want to keep in on the water and I need to trailer it. I’ve been sketching a design where you would disassemble the two hulls from the center living area and have both trailerable. Any ideas yet on this subject since 2008?

[redreuben]

Chris,

Have you looked at Kurt Hughes designs?

http://www.multihulldesigns.com/desi...ock/power.html

[blackdaisies]

I'm looking at this one, not a professional at all about boats, a newbie still shopping, but this one is clearly time proven. It has sail and power capabilities, dismantles, and is trailerable.

http://www.hartley-boats.com/lively28.html