Is it really that crazy? Motorsailer to powercat conversion

Hello all, longtime lurker/first time poster here. I am curious as to the opinions of the users on this forum regarding the feasibility of my plan below, and whether it would result in a seaworthy vessel or not. Also, this is just an idea in my head, any actual undertaking of such a task would be 5+ years away. But it never hurts to plan (i.e. dream).

The idea:
-Taking this cat (or one like it) and chopping off the rig and sails, replace with a new propulsion system and make appropriate changes to props, electric systems, etc. (edit: this is a Crowther 63, built in 1996, 30' beam and 4.8' draft)
-What I am looking for in an end product is a seaworthy ship that will serve as a viable liveaboard for mainly coastal cruising. Though I'm also keen on the ability to make an Atlantic passage once or twice.
-Absolute speed is not a necessity, but hoping for efficiency at comfortable cruising speed of say 15 knots.



Challenges
-I understand that sailing cat hulls are supposedly designed differently from powercat hulls. Hoping someone can elaborate on this.
-Doing this will make the ship aft-heavy. But can redistributing weight toward the bows help offset this? ie relocating tanks, battery banks, etc.?
-The litany of calculations required since this is a custom job.
-Cost. Well, naturally right?

I am sure there is a ton missing but I'd like to get thoughts as to how nuts or sane this plan would be.

 

Why not start form scratch? Seems you'd be throwing a lot of expensive boat away

Yes a power cat hull is very different from a sailing catamaran. Same as a trawler yacht looks nothing like a sailboat.

In part (and simplifying) because there is more weight aft on a powerboat (bigger engines/tanks).

In part because all boats squat at the stern under power and you need to try to offset that effect.

And partly because, unlike sailing boats, powerboats tend to run at certain fixed/known speeds. So you can be more specific in the design and aim for (in your case) a hull optimised for 15 knots, rather than one that has to be efficient as possible over the whole speed range. There are other reasons but those are biggies

The transatlantic range will be the big design factor, as you would have to carry, say, 2T of fuel. That will imply a much bigger boat than you might need if you were only coastal cruising

You can cruise along the Gulf coast to Florida, then the Bahamas and island hop down to S America, through the Panama Canal and then north or south yet no passage is longer than 80 miles - I've done it all in catamarans except the Gulf part. So do you really want to go trans-Atlantic?

What size boat are you looking at, what is your budget?

Richard Woods of Woods Designs

www.sailingcatamarans.com (and a few powercats)

 

Appreciate your insight, Richard. I am thinking a cat in the 50-60' range. Budget is up in the air. I guess that is why I am trying to assess my options. Could be between $300k to as high as $600k (it will have to depend on the outcome of some investments). My aim is to have a better cat then add the creature comforts as the budget allows. The liveaboard aspect for me and my wife is important as is the ability to comfortably take on other friends/family. And as I am a tall gentleman, I would prefer a larger layout (again, obviously if the budget allows).

Also, I guess if most of what I am doing is coastal cruising then designing the ship based on the potential for a transatlantic voyage wouldn't be wise. I would like to cruise such as what you described in the Americas, but also eventually Europe and the Mediterranean (I suppose it would make more sense to transport the boat in that case).

However, I guess I'm still wondering if whether redistributing weight from the stern towards the bow (particularly for the tanks and batteries) could mitigate the squatting you point out.



As a side note, Richard, I have been thinking about your Skoota 20 as an entry into boat construction. Though, not sure if I should just save money for my bigger endeavor.

 

We drove down to the first Port Aransas Wooden Boat Festival in October last year (ha, first time I've said that in 2015). For this years event we are thinking of bringing our Skoota 28 down to exhibit. It comes apart and is then road legal without an escort.

After that we would do the Gulf/Florida/Bahamas cruise I mentioned in my previous post. There aren't many cruising boats that can be shown at a boat show in the PNW (the Port Townsend WBF) and then 3 weeks later be displayed at one in Texas, and be lived on at both shows.

Moving weights won't help much as the CofG of the weight has to match the CofB of the displacement. In other words, at rest the boat would probably trim badly by the bow and anyway you want to centralise weights as much as possible to reduce pitching.

Not wanting to put you off but: Apart from the cost of fuel used you will need major maintenance expenses once you go to Europe, which make shipping it an attractive option. Otherwise you'd need to go say New York/Bermuda/Azores/Portugal. Or head north, via Greenland and Iceland. And assuming you are an American you should check out the tax and immigration problems involved with cruising in the EU (www.noonsite.com is a good place to start). And of course there are few places where fuel is as cheap as in the US, diesel is about USD10 a gal in the UK

If you are planning a boat that big, risking your lives on it and, presumably, spending a big chunk of your savings - why bodge it??

Richard Woods

 

The converted sail cat could turn into a hobby-horsing horror show when it is run directly up-wind, a situation the sail version does not encounter.

 

lazyrabbit, most sail cats have more than ample power to begin with. The engines, gears and drive train are already matched to the boat. Why mess with a good thing? They are also very efficient due to the easily driven hulls, Again, leave it be. Extra tankage could be located close to midships this should keep it on its trim. I imagine removing the mast will effect the trim this could be offset with added fixed ballast without too much negative effect. As for heading directly into the wind, head off a few degrees till she settles down a bit. Why don't you want to sail? Sailing cats are fast, safe and stable. With that kind of money you could surely find a classy ride.........g

 

Mr Woods mentioned the cost of fuel, have you thought about this ?

Pardon me if this is presumptuous but how much boating have you done ?

Sail boats make a lot of sense for long distance travel because even the most efficient motor boats require quite a bit of fuel. A sailing rig is far from cost free but for LONG passages they are much cheaper. You also have to factor in throwing the engine away every X miles. Running constantly for 1000's of hours to do passages like that they are eventually worn out, and bigger engines aren't cheap.

I haven't run the numbers for what you are suggesting, but as I'm getting older I did consider buying a motor cruiser and giving sail away. The fuel alone for a 4000 km round trip each winter is crippling, but chucking the engines every say 7 years...that was on a 30' boat or thereabouts, for 2 people...

As suggested the conversion is problematic but you could avoid some of the issues if you were happy enough with the relatively small yacht engines. Much slower, displacement speeds, but less fuel and engine costs..and the weight squatting etc. But then I'd wonder why you wouldn't leave the rig up and hoist sail when your well clear of land ? You can cover big slabs of a long passage like that under sail without much skill, effort etc. Sail the soldiers wind

 

With regard to removing the masts, there's no law that says you have to put up all the sail area the boat will carry. Small sails will be easier to handle and give you a get-home capability at the very least. If you keep the sail area modest, the chances of capsize are virtually eliminated. Masts also give you better range for your electronics and have other non-sailing uses. So you might as well keep the masts and just not use the sails if you don't want to.

With regard to cruising at 15 kt, my 34 ft cruising trimaran is quite happy at 10 kt under sail, and it used to motor at 9 kt in flat water (before I had to replace the motor and couldn't find with the same power that would fit the mounts, forcing me to cut the power by 25% and my speed to 7.5 kt). Just scaling that up to 63 ft, means your candidate boat may already have close to a 15 kt cruising speed if it's augmented a bit with power. Larger fuel tanks may be all that you need to shift the duty cycle to more power and less sail.

I think a great many cruisers are like you - they just want to live on their boats and cruise to different ports at an affordable cost. There's a reason why most cruising boats are powered by sail, with a modest sized auxiliary engine. It's the most suitable combination for the purpose.