f27 ama to short g32

I have 2 unglassed cedar strip amas, ostensibly for an f27 type trimaran (got them free a number or years ago). I do not want to build an f27 type tri (too much work) and I do not want to be overly "consumptive" in our deteriorating world by building any substantive boat from scratch when good parts exist. I am considering using the amas for a short g32 type boat with water ballast and a bat wing junk or similar rig to keep the CE low. I also have plenty of other parts, e.g. 10hp electric outboard, rudders, etc.

Thoughts?

When responding you can take into consideration. I have owned a MacGregor 26x, Oday 27, 40ft sailing cat (lived aboard), 60 ft sailing cat, and a Downeaster 35 sailing monohull. The intended use is trailer sailing and weekends on lakes or the Gulf Coast of Florida and Texas. Not looking to win any races! We are keeping our 40ft cat for costal sailing in the PNW.

I have done a ton of reading on boat design but can't find helpful stuff on the hydrodyamics of f27 amas vs similar bespoke catamaran hulls.

Thanks!

 

Can you post a photo or two of your hulls please Simon?

Have you estimated how much buoyancy they might have (approximately) at what might be a suitable load waterline, re building a cat with them?

 

Going to take a couple of days to get the hulls out from under storage for pictures. I estimate on average 26 ft long x 2 ft high x 1 ft wide. (Max is about 2.8 high and 1.8 wide. Min is about .5 x .5 x .5.) So, about 3,200 lb total buoyancy each. The aft ends look like they are about 1 ft above deepest part. I will assume they are designed to leave the water at that point. On average about 26 x .8 x 1 so about 1,290 each at DWL. If anything my estimates are high. May be as low at 800 each. Searched high an low for official numbers and can't find them. Once I get the hulls out of storage, I can get better measurements.

I have considered extending the tops a foot with ply to get some more freeboard.

 

If they are indeed based on F27 amas, they are probably of a lighter displacement wave piercing design compared to the modern high volume hulls.

Farrier always recommended paying close attention to the leeward hulls of his early designs for indication of how hard you were pressing the boat. They were designed to submerge and slow the boat to allow spilling of the sail as a safety precaution if over pressed.

I think modifying them for more freeboard might be a good way to go since they will perform fairly well partially submerged.

The only other issue I can think of is that they likely have very little volume in the stern, so deck/cabin placement will have to be farther forward like the G32 design you mentioned. On that note, I’ve seen a few Stilletto and Consers that have been converted to power/cruisers and they all sit very low at the stern due to the added weight.

Recently there was a Nacra 36 for sail here in Hawaii that had been extensively modified with a hard deck and cabin combing that was said to perform quite well despite how little volume the hulls had and how much heavier it must be. You can see they added freeboard in a similar way.

 

Thanks SolGato. Nice video!

 

You might already know this, but it is relevant so I feel the need to say it.
-the G32 is deceptively simple looking, but is very complex
-moving water balast
-mast float
-shifting standing rigging for self righting
-wave piercing hulls

I point this out because the boat you are describing will be screaming "faster, faster!" when it flops over. The design speed of the hulls is much higher than the righting you have. At the very least, I would not get too cute with the rig. Get something well sorted that allows one person to precisely control attack angle and twist continuously.
You might compare the full bag of tricks mini g32 you propose to a stupid simple tri or pod-cat that folds onto the trailer.

 

Very much agree. Plan to underpower with a low aspect rig if I do this. I am considering the tri thing ... although it is a bit more build.

 

What I was trying to imply is that if you go with a max beam of 9ft you need a plan for self-recovery from capsize. Go wide, maybe not.

 

now that I have them put of storage I can revise the max measurements and rise.

27.5 ft long
2.8 ft high
2.1 ft wide

stern 16 in
bow 6 in

max displacement is 10ft from bow

revising my estimate at estimated DWL of 1 foot, average beam of 1 foot and length of 27.5 I get 27.5 cb ft x 62lb = 1,705 lb each so 3,400 lb. If I assume I am over by 20 percent this is still a good bit more than Bernd Kohler's Maxi The Cat (a tribute to the g32) at the same 26.25 feet.

I think the next step would be to glass them, install cross members and float to figure out rest of balance ... If it does not work I go to the larger effort of building a tri with minimal loss ...

 

F-27 outrigger hulls are very fine in the sterns, so probably not catamaran hulls. You could do a very simple trimaran if it didn't need to fold.