Catamaran Bigger Engine Options

[Catpower]

Hi All

You may think me mad, but owing to a permanent semi disability in my right arm/shoulder now, I am unable to sail, only operate motor cruisers. My wife and I generally go out to sea on our own where we currently live.

In the Caribbean, where we plan to move to (St Vincent & The Grenadines, predominately known for sailing I know and winds during winter season) I have a bizarre idea and plan to buy an old 45 ft Cat, remove the mast & all sailing parts, transform the roof to sun lounging/bimini hood, and use it for cruising the Grenadines under power.

Hence I would like to put larger HP engines in to enable to me to cruise at 15kts, top speed 20kts in calm conditions if not more, and if this was theoretically possible re the hull (non planning) and also space available in the hulls and weight ratio altered at the stern.

..... Of course if sea state and winds preclude these speeds anyway then that is fine, but to be able to achieve them with more HP given they don't.

Of course fuel tank would potentially need increasing dependant on the engine and consumption, so realise there are issues, just wanting to know if it is theoretically possible and to what size engines I could go to. Also someone recommended getting old tractor engines, not sure if that works as an idea and more cost effective/less maintenance ...

Would anyone be able to offer me any ideas/advice or knowledge of such to achieve my goal? and what size I could potentially go to and what speeds I may achieve with wind behind me and calm sea state.

I am budget restricted, looking to in theory find an old Cat with broken or no mast and do a self internal and cosmetic refit and find someone to deal with the engines and Mast if it does have one.

Thanks anyone out there for their input.

(and of course if anyone has or knows of an old vessel (or suitable engines) somewhere in the Caribbean for my project do let me know!)

[tkeithlu]

That's going to be a huge project, taken on with a bum right arm. Even just the engine conversion will be daunting, because the designer will not have left any space around the engines that could have been put to uses that sell boats, and all the hoses, cables, through hulls, wiring, and engine mounts will be designed with one type of engine in mind.

Consider starting with a power cat.

[rslifkin]

If wanting a slow boat, this would be reasonable to do. But if you want the extra speed, I agree, you'll be better off starting with a power cat that already has engines sized for higher cruising speeds.

[Snore]

I would ask the manufacturer. My bar-napkin-engineering analysis shows added stress on the bridge deck and engine mounts. The amount of added stress may exceed designed stress limits.


Of course the liability of this engineering study is capped at my fee.

[Dsanduril]

You may want to turn the thinking upside down and look at the day charter catamaran market and then do an interior build. Many of these are delivered with engines that allow them to do 15-20 knots with 30 people on board. Finding one in the 45’ range might be the hard part. There’s an entire fleet of Gold Coast Yachts (built in St. Croix) day charter cats in Lahaina. They all do 15 knots easy, but don’t have much in the way of accommodation. I’d at least look at that market to see if the project would be easier than the other way round.

[atoll]

just buy an old charter cat with working engines and broken mast or remove the mast and mount a longshaft 240 hp outboard in the center when you want to go faster,a couple of fuel tanks in the bows should offset the weight of the mast and new engine.....

[Cadence]

A sailing cat is designed to sail at hull speed. Adding high HP is folly.

[lhuff35204]

We bought a 38 ft charter power cat with twin 110 Yanmars. It only does 9 knots, so you'd need to go bigger than that. Most of the power cats I've seen are underpowered. I wouldn't buy another charter, it was abused and poorly maintained to keep it in constant charter.

[SteveSadler]

A charter 56' sail cat here in hawaii had 2 85hp Perkins and would so 15kts. I imagine you'll find bigger engines would fit, but with displacement hulls doubling the hp may only get an extra 5 kts. I built a 24' power cat and tested it with a 50hp outboard getting 12kts, with a 115 I got 20kts. Foils would give you 50% more speed and fuel efficiency. If it has daggerboards you're halfway there.

[chrisr]

if you want to cruise at 15-20k, suggest to get a power boat (mono or cat hull) which is designed for these speeds

sailing cats are not

the main question is weight. we are sort of towards where you want to be - our cat has 2 x 55hp turbo charged yanmar 4JH's and can carry 750L of fuel. this on a 7.5mt 40' cat.

we can motor at 10k but unless super flat water the pounding and vibration is most unpleasant, and fuel consumption is pretty high. on the plus side we only ever use one engine and can motor into 25k headwind at 6k on that

but for this limited advantage the boat does sit several inches lower at the stern than it should and this limits other provisions & equipment we'd like to carry.

on balance i'd rather smaller engines & less weight...or the same engines on a bigger boat !

cheers,

[clakiep]

The idea of a fast powercatamaran that also sails is a interesting but completly new project. You better get a good designer and naval engineer on the drawing board to work on it. I worked on a 24' daysailing cat project, cruising at 20+ knots with 80 HP outboard for waterskiing and moderate sailing performance with a wingsail rigg which is still under construction. For a bigger liveaboard cat careful considerations for speed, power, weight, payload, endurance and sailhandling will be nescessary. Any more info mail me at clakiep@terra.com.br

[carlosproa]

So
Budget and speed past 10 knots don’t go together.
However, any old displacement catamaran may need to be placed on a diet to shed weight and be able to achieve hull speed.
For more speed than that then you probably want to think of hydrofoils that lift the water length a bit height and reduce friction. I would be nice to have modern hydrofoils with surface sensors, but a low tech version of inverse triangles foils would do the same at a considerable less cost. Think of Dave Keipper type of hydrofoils design.
Another option fir a mast less catamaran is to use wind power via a 4 or 8 lead kites. There are plenty of proven design.
Lastly, you could build a Harryproa which is basically a type of pacific proa. Google him and see his designs.