Trimaran - Especially Searunner - Owners

[longjonsilver]

Originally Posted by catsketcher

Try to not bolt anything through ply. I use strands of uni to stitch fittings on. This reduces bolt holes in ply and because bolts and ply don't really like each other bad things can happen. I have composite new attachments, jib tracks, motor mounts, motor mount hinges, genoa block attachments and more. You can update the accessories and she will be better, cheaper and look more modern too. But composite chainplates are the real deal and if you aren't good with metal, will save lots of money and time.

Can you tell us more about attaching to ply without using bolts and also composite chainplates?
thanks
jon

[catsketcher]

Gday Long John

Last weekend I had my cat on the slip. She is strip cedar for thew curved hulls and ply for the bulkheads and decks (with a foam cabin and a Duflex aft deck)

I had an issue with the pivot for the motor. It is a 12mm stainless tube that runs through composite tubes that are attached to the hulls. Normally you would bolt the tubes onto the ply bridgedeck bottom but I used uni tows and stitched them on.

I started with two 10 mm holes in the ply, either side of the tube section. Then I got my uni tow. Tow is the stuff they make glass fabric from. I got mine from a friend but you can buy a large roll cheaply at a surfboard shop. It is the stuff they feed into choppy guns. I fold the tow over a few times to get it down to a manageable length, about 1.5 metres or a bit longer. The I thread one end through a large plastic needle (from a craft shop).

Next step is to saturate the tow with epoxy. I lay it down on scrap ply and wet it out with resin. You don't need it wet, it will be going over other tow so keep it a little dry after wetting out.

Then I go to the boat and just tie it on (without a knot). Up and around, then down and around, just like you would do if you were tying it on with string. Pull hard every turn round. Be careful to keep the needle to the outside of the bundle as you lay new stuff on.

To finish you can cut off the end and push it into the now thick snake of unis wrapped around your fitting. A little glue mix and some double bias placed on top is a good finish (do it all wet on wet) but I didn't do this on the weekend.

The reason I like it is because I never have to get anything made by a stainless guy, I have no bolts which can be a source of water ingress and rot, it is surprisingly strong, and because epoxy loves ply, it is waterproof, with the addition of a little filler after you have finished stitching.

My genoa track (which is really just a piece of PVC tube with two layers of 600db tape over it and notches cut in) is connected onto its supporting member under the deck by about 6 turns of stitching. I had a motor pod (with a 25 four stroke) held on its pivot arms by about 8 turns of stitching on each hinge.

I would recommend that you get a nice 1cm diameter thick snake (which gets squashed sideways when installed) when you are doing a high load part. That said, I have never broken one.

My folding catamarans have stitching everywhere on their hinges.

If you want an even easier method, and stitching aint hard at all, then you can buy a big rounded captive shackle, drape lots of 2.5 metre long tow over the shackle middle (open the shackle first) and then feed one half each side of a bulkhead and wet out. Instant chainplate. I use this for lower loads than a real chainplate - say my genoa blocks (which get a high load from a pretty large genoa). I just fed the tow through a hole into the interior of the cabin and spread out the tow and wet it out onto a bulkhead. Seems fine still.

As for real chainplates, the best way is to use about 100mm wide unis. Cut a piece of stainless tube about 100mm long and epoxy it onto a ply pedestal about 20mm high above the deck. (Line the whole thing up with the load first)

Then drape 100mm wide uni tape over the tube and down through slots on the bulkhead. Fan out the tapes as you go and make sure there are no bumps in the bulkhead. I use 2-3m long pieces of 100mm wide uni so that I get more than a metre of coverage each side. I find that about 8 layers of 600gm tape is good for a small cat, but I would have to do some calcs for a bigger load. (Actually I would look through some plans too)

As to the split in the chines - what a duffer. Searunners have no chine logs. So it is probably split glass. Get in there with a 4 inch angle grinder and remove all the split chine glass. remove some paint on the outside away from the area and then redo with epoxy and 100 or 150mm wide DB tape, whatever fits between the chine stringers. (Be careful of cutting your own DB tape from the end of a wide roll - it concertinas something awful.)

cheers

Phil

[migizi]

Exciting stuff guys! Composite chainplates? now that sounds sweet! but maybe a bit over my skillset (for now).

Reading through alot of the now "old" posts on here I've got a number of upgrades in mind, many of them will have to wait. Technology certainly has changed alot in recent years hasnt it? What exciting times!

First thing I'm considering is lightweight CB, this stage of build is probably the perfect time to change/modify the board that is already made.

I've acquired a handful of the suggested books to my collection of "boat stuff" books I've amassed over the years.

Construction manual (updated version)
The case for the cruising trimaran
among the multihulls
Epoxy basics by Russel Brown
Gougeon brothers on boat construction
backyard boat building for the 21st century

As well as taken down pages and pages of notes directly from this thread concerning updated taping and glassing methods. I've done a bunch of glass work on our rental boats, should be plenty of experience to get me started when its time to get itchy again!

Just the other day I came across the photo of the tri with one removable ama, now thats something to behold! We may not go that route, but who knows yet?

Seen photo's of one being cut for transport, looks like it was cut about 3' out from the cabinsides. Still have yet to find a write-up of putting it back together. Weather I find that info here or not I am still going to consult marples when it comes to important things like this.

Very excited to learn a whole new set of tools, As I know my way around a mechanics toolbox with my eyes closed, wrenches and sockets tend to get a bit boring...

More to come soon!

[Buzzman]

Joining the cut off ama back to the wing is the same principle as Phil outlined above. Use butt blocks.
Basically, if you put to pieces of timber together with nothing but glue between them, this is a 'butt joint'. If you add a pice of wood or ply across the join to strengthen it, this is the 'butt block'. it's strengthening the butt joint. Normally, off the boat, and in a good workshop, you'd probably join two such pieces of ply or timber using a sloping scarf joint. But this is impractical in an already built structure.

Essentially, use a strip of similar thickness ply, glued to the underside (inside) of the cut line such that it is 50% on one side of the cut and 50% on the other side, acts as a butt block for the cut re-joining
So if the cut in the wing deck is 1.5m fore to aft, then maybe a strip of 9mm ply 1.5m X 400mm would give 200mm either side of the cut. This new piece you're adding is the butt block.
Basically glue and clamp to one side, then push the two boat sections together using thickened epoxy in between every mating surface. You will probably have to use 'temproary screws' to get the second section (the ama) to join tightly with the butt block. Remove the screws and fill the holes once epoxy goes off.
If you 'feather' the edges of the butt block (like plane them back to a 1:12 slope as though for a scarf joint), then you can also add fibreglass right over the whole join once rejoined, if you want to be certain the joint won't tear open again.
A couple of layers of 600gsm or 3 layers of 400gsm double-bias would appreciably stiffen the join that the butt block has already stiffened.
What do you think Phil? Would a butt block top and bottom inside be 'enough' or would it be safer to add some glass as well..??

[longjonsilver]

Originally Posted by migizi

Seen photo's of one being cut for transport, looks like it was cut about 3' out from the cabinsides. Still have yet to find a write-up of putting it back together. Weather I find that info here or not I am still going to consult marples when it comes to important things like this.

i called a guy in Bellingham Wash that was selling a 40CC and he told me that the amas were cut off to haul it to the water then reattached. Marples knew about this and approved it. Best to talk to Marples directly, it wud be worth your coin to do so, if you do plan to move her to the water.

jon

[catsketcher]

Originally Posted by Buzzman

Joining the cut off ama back to the wing is the same principle as Phil outlined above. Use butt blocks.
Basically, if you put to pieces of timber together with nothing but glue between them, this is a 'butt joint'. If you add a pice of wood or ply across the join to strengthen it, this is the 'butt block'. it's strengthening the butt joint. Normally, off the boat, and in a good workshop, you'd probably join two such pieces of ply or timber using a sloping scarf joint. But this is impractical in an already built structure.

Essentially, use a strip of similar thickness ply, glued to the underside (inside) of the cut line such that it is 50% on one side of the cut and 50% on the other side, acts as a butt block for the cut re-joining
So if the cut in the wing deck is 1.5m fore to aft, then maybe a strip of 9mm ply 1.5m X 400mm would give 200mm either side of the cut. This new piece you're adding is the butt block.
Basically glue and clamp to one side, then push the two boat sections together using thickened epoxy in between every mating surface. You will probably have to use 'temproary screws' to get the second section (the ama) to join tightly with the butt block. Remove the screws and fill the holes once epoxy goes off.
If you 'feather' the edges of the butt block (like plane them back to a 1:12 slope as though for a scarf joint), then you can also add fibreglass right over the whole join once rejoined, if you want to be certain the joint won't tear open again.
A couple of layers of 600gsm or 3 layers of 400gsm double-bias would appreciably stiffen the join that the butt block has already stiffened.
What do you think Phil? Would a butt block top and bottom inside be 'enough' or would it be safer to add some glass as well..??

I would be thinking of butt blocks on the deck and underwing panels inside the wing and maybe under the wing. I like the idea of feathering the edges. I would probably go for just the glass on the deck.

That only does the deck and underwing. The stringers run fore and aft on the wingdeck so the position would be determined by these, placing the cut in the middle of a set of stringers. The really interesting part is the main strength bulkhead.

I am thinking, if this were my boat, I would cut away a section of deck at each main strength bulkhead join (or underwing if you like working upside down). So four largeish ,say 20 x 20cm square holes (with rounded corners).

Then when the boat gets squished back together you can then install long, really long, 600mm butt blocks on each side of the main strength bulkhead. I would increase the thickness to about 12mm because the top and bottom stringer of the main strength bulkhead will be cut. It will work fine in compression but not so well in tension.

So make the butt blocks for the main strength bulkhead nice and super long, as you cannot exceed the shear strength of the epoxy. I would sand the whole shebang when it is cut off. I would be wary of gluing them on one side first because I would like heaps of time to get the amas set up perfectly with no worries about misalignment of the main strength bulkhead butt blocks.

I would prefer to get the whole shebang well sanded and then get her exact and only then glue butt blocks in. So for me I would make all the butt blocks and place them in the cavity before assembly. Make access holes in the outer cabin side, large enough for me to get by hand in with epoxy on a stick. Then I epoxy the underwing and the bottom of the long butt block (gooping the thing from the access hatch (that will be fun), position the long butt block (running fore and aft between stringers) and get a friend to start screwing in from underneath with plaster screws. Clean up, (it is going to be a mess, use lots of disposable rags) and then do the same for the deck butt block.

Actually that is really dumb. If you have the two squares at each end to butt the mainstrength bulkhead you would just use flexible enough ply to get everything all glued up and then push the butt blocks to the underwing, the deck and the main strength bulkheads. Not hard at all. Clear epoxy the lot. Then you put little butt blocks around each square and put a lid on and then glass every seam. The deck and underwing butt blocks do not have to be continuous, you are going to glass these guys too. So you can have maybe two or even three running fore and aft, but only one for the MSBs.

Because I would like to be sure, I would run some unis along (sideways) the main strength bulkhead on deck and the underwing. Grind these out before she gets put back together - just get back to glass or scuffed epoxy. This would help the main strength bulkheads do their thing and would not weigh much.

Whatever you do, DON"T use mechanical fastenings (except for the temporary screws). Using butt blocks, db and uni tape will make a much stronger, stiffer and less stress concentrating structure. There is no need to use old tech even though the design is a classic.

Keep us up to date.

[Roy M]

Status update: the mast halves are assembled, radar strut installed. Time now to assemble all the toys for install (lights, electronics, some more lateral sheaves for the dinghy hoist,etc.). At the same time, I decided to replace ALL the standard service parts in the Edson steering pedestal. Needle bearings, nylon washers, chain, etc. Edson recommends this every 7-10 years for Pacific boats, every 5 years for service in the Caribbean, Florida or tropics. It's about crevice erosion in stainless. Losing steering or engine controls is fairly common in boats that cruise, so, out with the old...

I have to have the steering completed so I can go pull the stick. Once it's off the boat I can install the new mast step, which is slightly larger than the old one. Since I have more electrical and electronic stuff in this 2021 mast, I have to take care to make all that stuff will fit through the centerboard wall and enter the mast step when the new mast gets installed later in November.

Then, it's time for the last of the exterior projects: deck repairs, removal of old nonskid and replacement with non-sand grit from AwlGrip, resealing the float hatches, reinstalling the windlass (which I had an electrical shop inspect and service), and replace the lifelines with Dyneema. Then, as our rainy season begins in January, I will finish the galley remodel and other interior projects not finished earlier. By the launch anniversary of March 21st, I hope to be ready for testing and seatrial. First, though, the sails need to arrive. The dodger and Bimini, as well as the sails, will be formally ordered as soon as the mast is stepped. Two to three months wait is the new normal in post (I hope) Covid/supply chain America. The hope is to have a departure window in May. If that doesn't work out, there are worse places to be than California's Channel Islands, and, later in the fall, Baja California's Sea of Cortez. It's good to have options.

[migizi]

https://www.youtube.com/watch?v=2XF3mbZ6AJA

[migizi]

https://youtu.be/fvuzhmO5aiw

[migizi]

https://www.youtube.com/watch?v=idpNP9GnTx8

[migizi]

https://www.youtube.com/watch?v=i3TU2MnynkU

[migizi]

https://www.youtube.com/watch?v=fvuzhmO5aiw

[catsketcher]

That is a lot of black wood.

[longjonsilver]

Originally Posted by catsketcher

That is a lot of black wood.

Do we believe the black wood, or the nice pinging of the hammers?

jon

[Cavalier MK2]

Wash and clean, DRY OUT, ping with hammers, press with screw driver, take core samples where necessary. Replace what is needed.. Often old leaves and residue will stain as well as water ingress.