We have been getting some things done as well. Our first task was to go retrieve our cars. We ended up renting a car to go pick up the one we left in Hammock Beach, a two day trip. Then we drove up to my friends house near Baltimore to get the other car out of his way. With the heat it was nice to be in air conditioned cars even if it meant a lot of time sitting in cars.
One of the first items after we got back to the boat ended up being the raw water pump for one of the air conditioning units. It had been having some issues and finally died before we left Hammock Beach. I had even picked up a replacement at Sailor's Exchange in St. Augustine as part of a trade deal we did for my old CQR anchor so I was prepared for the job. With the heat, getting it installed quickly climbed up to the top list.
Another water leak was discovered during the rains while we were at anchor and the leak managed to short out an AC electrical outlet so we got that replaced as well. I also worked on my eye splices again as I had to create one for a replacement spinnaker halyard that had started fraying during the trip north. My wife washed the boat one morning and ended up getting a bit of a sunburn in the process. We have been trying to keep to more indoor tasks until more "normal" temperatures return. I've been watching the local pawn shops to see if I can find some fishing gear at more reasonable prices.
We've been researching options for building the hardtop as well. This is the item that has my brain spinning at the moment. Trying to figure out what materials to use to build the top at a reasonable price while producing a quality result. Do I use marine plywood as a core, or balsa, or something more exotic. And what thickness is needed to produce a top I can walk on. And what substructure is needed. Right now I'm leaning towards marine plywood core for cost and availability encapsulated with a biaxial cloth epoxy fiberglass. The top will be load bearing itself, bolted to the arch at the back and using four "legs" to hold up the front end. At least that is the current theory.
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| Some rough mockups of the top |
So, that is what we have been doing the past several days, and I'm sure it will continue for the next several days as we try to hide from the sun and oppressive heat for the next couple days.
Hi Mike,
ReplyDeleteI have been thinking about the same thing (planning for when I have the boat). Here is my thinking.....
The type of resin is really a personal preference, however I find Polyester resins better to work with as wetting out the cloth is much easier. Chopped strand mat on outer layers will give a better finish, and the final layer on each side should be 300g.
Ply can be made to be strong, and if I was going to make it out of ply, I would use 3 layers of 4mm ply, and bond them together with a very over wet layer of 600mm chopped strand. Using 3 layers of ply with glass in between means it can be molded to the curve required using simple frames, and bonded in that curve (doubt you would need stringers, it will be bullet proof). I saw a coach house of an old timber motor boat replaced using this method, and as the new owner was tall, he wanted no stringers to give extra headroom. The disadvantage is solution is the weight and that if water got in, it can wick along inside the ply.
End grain Balsa is very light and easy to work with but it does require a mold to be made. The mold can be a simple melamine finished structure made to the desired curve. The advantage over ply is the weight saving, and that water ingress cannot travel beyond the small block of balsa (assuming it is set in correctly). The disadvantage is the more complex mold and it is expensive.
My preference is to use 12mm Kleggcell. It is very easy to form into the curve needed to match the arch, and even alter the curve to match the coach house curve. Using sacrificial pieces of ply cut to the curve desired, and using a strand of glass as a thread, tie the Klegg onto the ply. Once you have glassed the top, cut the threads and remove the ply. Then glass the bottom. Stiffening ribs can be added to the bottom using a low density foam, or better idea would be 24mm conduit cut in half and glassed over. This will give you built in cable pathways for lights and solar panels etc. This is an light weight, mid range in price, and as the Klegg is closed cell, no water wicking.
cheers,
Alan
Hey Alan,
DeleteYour ply schedule does sound heavy. My thought was that ply would be providing some structure...unlike foam or balsa...so that less would be needed (3/4 non-marine plywood is used for flooring in homes, etc.). Weight is definitely an issue on the catamaran.
One of the problems I'm having is getting useful engineering data on load capacity, etc for various core and skin thicknesses of various materials. I know the information has to be out there...but with the slow internet here at the marina, I haven't found it yet.
My theory (hope) was that I could make the top by constructing a model using the core material and then just glassing over the model to create the finished top. Given that the top side needs non-skid on it and the bottom could be "textured", I'm not too worried about the overall look or need for a mold.
I think foam would be the ideal way to go, but haven't found data on the rigidity of the foam panels. Jamestown claimed the Divinicell panels are rigid and couldn't be bent like plywood can. Having never seen the stuff in person, I'm not sure what to think but as minor of a curve as I need I would think most things (even 3/8 plywood) can manage the bend.
I really need someone with a bit more experience with such things than I have to provide some additional guidance. Still looking for that though. ;-)
Hey Mike,
ReplyDeleteOn the bimini project, check out Azek Sheet fiberglass panel board. I was thinking of going with a hard bimini for a while and that seemed to be the most cost effective method I found.
Here is a link to a catamaran that did this with lots of photos. http://www.cruisersforum.com/forums/f136/bimini-38307-4.html#post823942
Good luck and fair winds,
Jesse
Hey Jesse,
DeleteFrom what I could tell (pages only partially load...did I mention internet seems to suck at most marinas) those panels are PVC. To go that route (or Starboard...which I previously considered) I would need to have a new frame welded because the panels won't support my weight without underlying structure (the current frame barely holds up the sunbrella material and I want to be able to walk on the top). Hiring a welder and having them construct a frame and fit it to the boat to hold bolt on plastic panels gets a bit pricey as well.
My hope is to create a top that has enough structure integrated that I don't need a separate frame, just 3~4 struts at the front to hold it off the coach roof (I know this is possible since I've seen a couple boats that have done similar...but don't have insight into the underlying structure on those tops).
My big issue right now is finding appropriate engineering data on the various materials. Most catamarans are built with cored composites so I know they can be strong and light and there should be data out there...but the question is if I can find it. I've found numerous places that mention that doubling the thickness of the core increases rigidity by a factor of 4 or more...but no real base numbers such as what a 1/2" core of material X with two 1/8" polyester fiberglass skins can support over a 3' span supported on all edges.
I'm probably overthinking some of this...but I know I have a tendency to over-engineer things and I do know that weight is a concern on this project. Of course, so is the budget.
Hi Mike,
ReplyDeleteI checked a few sites on hard top biminis, the best one with most complete instructions with pics was hacking family who designed and constructed their own hard top bimini in Thailand.
Here is the link or location
http://svocelot.com/Ocelot/ThaiRefit/Bimini.htm
Might give you some ideas. I've contacted Jon Hacking in the past to ask questions and he is always helpful.
Doug from VT
Thanks Doug, I'll check it out.
Delete