45' solar catamaran

[yabert]

Hi
Few weeks ago we bought a custom made Lock Crowther Spindrift. The owner (builder) put a lot of time on it, but let the boat without interesting bedrooms, toilette, galley, etc. Almost everything inside have to be done.
The boat, 45x22', have narrow hulls... like 32'' wide at waterline. Should be ''fast''.
It's a plywood epoxy buid.
One of our goal is to put a large solar array of 10-11 kW on the boat and run this multihull with two electric motors and two giant batteries (like 150-160 kWh total).

About me:
I'm french Canadian (sorry for my english), I'm working with batteries and electric vehicles since 15 years, so I know what to do in this area. I weld aluminum, steel, stainless (Tig/Mig) and have a small lathe + 3'x2' CNC router.
But I have little knowledge about wood, epoxy and other boat building stuff.
So, I'm here to learn and have advices.

Few picture of the boat and a rough 3D of the plan.
Thanks

 

[rangebowdrie]

You'll have way more than enough time and money invested in that boat just getting the interior and exterior useable for more than just camping out for a weekend.
You, (and your wallet,) might be greater served by just mounting an outboard on the end of each hull and calling it good.

 

[yabert]

You'll have way more than enough time and money invested in that boat

Yes, lot of time. I'm already on the design phase and we plan to spend 1 year part time + 3 months full time.
About money, it look like most boat that size are 100k$-300k$, so there is place to spend before reaching such price.

 

[fallguy]

The boat probably cannot handle all that planned mass.

 

[kapnD]

The boat probably cannot handle all that planned mass.

That is my thought as well, and possibly the reason that there were no interior furnishings built.
Calculate the weight of the interior accommodations you want to build, add the weight of the solar array , batteries, motors and running gear, and see if it still floats.

 

[fallguy]

Catamarans are very weight sensitive and narrow hulls means more so.

She’ll end up well below her lines, probably why nothing was done inside. The calculations are really not needed. The boat wasn’t made for such changes.

The Crowther Spindrift also has something of a recall/repair requirement. Something related to the loss of one of them at sea. Double Arrow? Then they added gussets between bdeck and hulls, but I don’t know any details on how, or if this boat already has it done. She looks a bit rough. But if the boat was already a bit weak on bdeck supports in big seas, you cannot add mass above the bdeck in batteries and array and much furnishings.

It isn’t a terrible boat, but it also wasn’t made to operate far from it’s design.

 

[fallguy]

The Spindrift 45 design displacement is 11,500 pounds if built to original specifications.

No idea on immersion data; maybe someone else can guess it for you, but a wild bad guess is 800 pounds is an inch. So, for every 800 (or a better guess), the boat sinks an inch below her design lines.

Anyhow, keep this in mind or you’ll be very sad fixing it all up and adding 2400 pounds and sinking her 3” below her lines, or 4800 pounds and 6”, etc. or if I am wrong about immersion guess and it is worse, or if the boat is already built too heavy, etc. Sorry to be the bad news guy, but I may be saving you a financial disaster, all the best.

 

[oldmulti]

The dimensions and build of this Spindrift looks like a Spindrift 40 extended to 45 foot with a Tennant canoe type stern added to the rear. The Spindrift 45's had foam glass hulls with plywood everything else. Spindrift 40's had cold moulded wood hulls with plywood every where else. The Spindrift 45 Double Arrow and at least 3 Spindrift 37's have had hull start to break at the hull underwing joint. The Spindrift 40 had much the same structure. Reason nis the underwing hull joint either required an additional angle panel from the underwing to the hull side heavily glassed in or on each full width bulkhead an additional 3/4 plywood circle placed on the fore and aft face (about 1.5 foot radius) to strengthen the joints. Do both if you are unsure.
If you are not going to put sails and a mast on this cat you will save at least 500 lbs but the weight will depend on how it is initially built. You can do some very light furniture but solar panels and batteries can weigh a bit. Do a weight study of not just the weight but where it is going to be positioned on the cat. PS a small talk to a boat designer may help as well.

 

[yabert]

Wow! lot of good comments here. I like it.
So, yes, hulls are narrow because they was originally for a 37' and the owner add length and the square forms at the rear.
Buoyancy was a first concern to me after our first visit. I drew a rough hull based on few dimensions as you can see below.
That give me a displacement of 3.5 ton (7770 lbs) at water line per hull, so 7 ton for the boat.
If I add 1'' that add 217 kg per hull, so 434 kG (955 lbs) for the boat.

There is two diesel 4 cylinders engine in the rear to remove + the diesel tanks.
Batteries will add around 2200 lbs + 300 lbs for motors/controllers. Solar panels and their support should be below 1800 lbs.
Anyway, for sure there is concerns to clear before investing time and money on it.
At the moment, investment is minimal or nearly zero if we sell few good parts of the boat.

 

[fallguy]

Well, much depends on the current weight and where she floats now.

Did you float it, yet? If she is on her lines now

I think it is a good deal, but am warning against overloading.

Did it get the gussets, yet? Maybe they were not needed for the 37’, but I would he worried the extension puts even more strain on the 37’ design.

Oldmulti brings the best comment to find an NA.

I am guessing this is Lake Ontario and so you only want a solar cruiser, not bluewater bound. That helps as well.

 

[yabert]

Boat is out of the water since 2 years now and this is the only picture I have from the boat in the lake.

Did it get the gussets, yet?

I don't know. I have to learn and see what is a underwing hull joint

 

[fallguy]

It is just where the bridgedeck (bit over the water) connects to the hulls. But all the more reason to find an NA and ask them if your structure is strong enough given the corrections made to these boats.

Consider, making the boat longer and doing nothing with bdeck connections. There is more rotational torque when one hull twists the opposite direction of the other. Given this is a known problem in the larger design; one would automatically be curious whether anything was done to the smaller design when extended or if the smaller design had even less connection than the original 45’, and thus by extending you are woefully inadequate for any big seas. I’m sure Lake Ontario can whip up some good seastates now n then.

And you can do some visual inspection that is less valuable than an NA review, but go look at all the connecting points and see if there are any signs of strain. This would be something as simple as broken caulk seams or cracks in wood to clearer problems. The issue, though, is not as good as an NA because the visual check only validates prior performance against unknown conditions. She may have never been taken out in 2 footers..

 

[yabert]

It is just where the bridgedeck (bit over the water) connects to the hulls

So, it's the part circle in blue on the pic below, right?

 

[fallguy]

I’d say so, but I cannot tell you if that is the/a modification or original.

 

[oldmulti]

The jpeg of the underwing is a modification. A standard Spindrift 37/ 40 had a near 90 degree connection at the wing deck hull joint. Look at the Spindrift 37 plans on Multihull Structure Thoughts (index on first page will guide you).