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Best Guess Trimaran - 2014

I thought I did a lot of work on Best Guess, my home-built trimaran, during the winter of 2012-2013. Well I did even more this last winter. I added 3 feet to the stern, built new amas, swapped out the 16 foot ladder with an 18 footer, cut the rudder down smaller, got new sails, and made a better boom. So much of this work really is best guesses.

The transom, after I cut it off.
 

My plans for the new stern.
 

The amas under construction. Multiple waterproof compartments.
 

Again, plywood underlayment for the skin with cedar stringers at the chines.
 

My intent was for narrow bows for a fine entry into the water.
 

Almost ready for glassing.
 

Here's the completed boat fresh out of the garage before schlepping it down to the marina. Nice new shiny amas and a longer ladder (cough) I mean aka.
 

From the side showing the swoopy lines of the amas. They're much higher volume than the Hobie 14 hulls I used before.
 

From the front.
 

An ama, showing how it's canted outwards.
 

Pin and strut system to connect amas to the aka. The old version needed no tools to assemble. It was just a matter of sliding pins in. The struts are better now as the old system resulted in the amas moving a little all the time. Now they're rock steady.
 

Detail showing the struts and mounting pins.
 

From the back, showing the new 3 foot tapered stern.
 

An ama.
 

Ama stern.
 

The new stern.
 

Forward ama hatch with foam seal and bunjie hold-down.
 

Middle ama hatch.
 

How the bunjie hold downs in the amas work.
 

Wood floor in a forward center hull compartment. This is where the port a potty will go.
 

Access hatch to stern storage compartment.
 

Sliding hatch with weatherproof upper lip.
 

Retractable rudder. I cut the rudder down in size from what it used to be for less resistance. It still works well. Note the steering tiller, and compare to what I ended up with below.
 

Cleats for keeping the rudder raised or lowered.
 

The seats.
 
   

And further refinements

After launching the boat with all these revisions I realized I made some wrong guesses. So I made some major improvements this summer. I've now run out of things to do for the most part except for re-installing my spinnaker. It sails very well. Neutral helm, great acceleration and points like a monohull. The first time I tried the speedometer app on my phone it read 12 knots. I know I've been quite a bit faster, so who knows what it'll do. We have informal races every Sunday afternoon in Liberty Bay, and since my improvments I've won every race by a large margin. On a good day there are 7 boats. My friend Paul with his Stiletto catamaran is the only other multihull, but there are some good sailors. Anyway, I'm really happy with the performance. My goals of the safe, dry multihull for the Northwest have been realized.

Best Guess moored, with the sail covers I had made by a guy I found on Ebay. I think his username was "comboat". Awesome quality on the stitching and details. I had him put a mesh panel in the bottom of the jib bag, and a pocket for a batten on the mainsail cover. The jib bag sure makes it faster to get set up since the jib's already hanked on.
 

Another view with the sailbags on.
 

Now with the sails rigged. Having a corner slip makes it easy to sail away from the dock.
 

Forward view.
 

From the stern.
 

I didn't take account for the heavier weight of the "new" Best Guess after I added 3 feet in length, a longer ladder plus a trolling motor and marine battery. As a result it sat lower in the water, and my amas also both sat in the water. Also the tails of the amas were lower than their bows. Traditional multihull wisdom says that one ama should always be out of the water, so I had to raise the amas and change their pitch. This meant drilling new mounting pin holes lower down in their bulkheads and then cutting off the excess bulkhead at the top. Here's how much I shortened them by.
 

My new daggerboard. My old daggerboard snapped off one fateful day while I was sailing in really strong winds, pointing on a close reach with only the main up. Sounded like an explosion, and I pretty much freaked out not knowing what it was. Seconds later I realized what happend and looked up. There it was floating away. So I made a new cedar core one with 2 layers of carbon fiber and 5 layers of fiberglass on each side.
 

The broken off edge of my old daggerboard. It only had 2 layers of glass per side.
 

So far so good with the new daggerboard. It hasn't broken yet, and performs really well. My boat points like a monohull. I put strips of oak wood on the leading and bottom edges for impact resistance. This may be the nicest thing I've ever made.
 

The new daggerboard is a little thinner than the old, and water came up through the daggerboard slot sometimes. I bought daggerboard slot gasket material from Annapolis Performance Sailing and it works incredibly well. Only a couple of bucks per foot. You glue it on with 5200 sealant and then cut a slit down the middle. It conforms perfectly to the contour of the daggerboard.
 

I re-did the rudder/tiller setup. After I added 3 feet to the stern I had attached a long pole to the strut coming off the rudder cassette assembly, and you pushed/pulled the pole to steer. It was totally unintuitive. So I ditched that, added a pivot point and made a connecting rod. This setup works great! I got a used telescopic "Battlestick" tiller too which I love.
 

Another view.
 

The rudder kicks up via 2 ropes and cleats when not in use. This way it doesn't get slime growth on it when not in use.
 

I also lightened up the rudder cassette assembly (note drilled out holes) and the struts for the steering connector rod.
 

A huge improvement was adding an electric trolling motor, a marine battery and a solar panel to charge the battery. The motor clamps nicely onto my rear aka (made from the extension ladder with the rungs cut out). I used to be afraid to sail this boat by myself because docking under sail with an 18 foot wide boat was really tricky. Now I can drop the sails and motor in. My new boat hook helps too.
 

When not in use it stops you from using the very back section of the starboard side seat, but this seems to be OK.
 

This is a Coleman brand photovoltaic panel, probably made more for RVs. It works well though. Since installing it, I've measured the voltage on the battery and it's consitently been at 13.2 volts. It cost about $100.
 

It came with a regulator that I mounted inside the center hull.
 

After borrowing my friend Paul's aircraft battery with one bad cell, I decided to buy a deep cycle marine battery. It probably weighs 50 pounds, and I mounted near the bow to better trim the boat.
 

Being 20 feet in length, Best Guess required navigation lights, so here's a close up showing the chrome light fixture near the bow and the on/off switch in a forward storage compartment with the battery.
 

Some rigging improvements were in order too. I repurposed my windsurfing boom adjustable outhaul lines to now be on Best Guess. You can bag out the main or pull it tight from either side of the boom.
 

The jib sheet fairleads and cleats are now located at the center of the front of the cockpit. They're really easy to operate now.
 

They're a little hard to see in this picture, but I have 2 lazy jacks plus a topping lift now that make dropping the main dead simple.
 

Lets not forget the humble port a potty. It lives in the storage compartment just in front of the mast. I installed floor boards, and made it so the port a potty locks onto the boat with a pin. This sounds weird, but it's really fun to use it. I've done it a few times while sailing solo. The boat has a neutral helm and stays pretty much on course with noone at the helm. You feel a little like you're on a carnival ride sitting low up front with the wind in your hair and the water rushing by a foot or two away.
 

My friend Paul while we're under way.
 

An ama slicing through the water in about 5 knots of wind.
 

A view of the Poulsbo marinia with the bridge to my dock section. My slip is at the far upper left under the right, upper corner of the flag.
 

You can see my slip a little better in this shot, again at the far upper right, right around the corner from the white motor boat.
 

My friend Paul's Stiletto.
 

A friendly neighbor at the marina.