How fast do sailing catamarans motor?

[Jimske]

Originally Posted by twohapence

Try a Yamaha 9.9 Extra Long Shaft high thrust or the similar Mariner. They'll give you more drive with a bigger prop turning more slowly.

LOL that's what I got

[Jimske]

I mean extra long shaft large prop part High thrust

[ZULU40]

Originally Posted by mikedefieslife

What a terrible video in terms of marketing. Thy really shouldn't have let Youtube stabilise it.

Anyway, about the boat. I imagine the cost of sails and rigging is a less than a 2 years fuel. 40 litres per hour is not uncommon for a motorboat.

Not sure this has been said, but in power catamarans there are basically two types, displacement (rare) and planing.

Expect planing boats to have a L/B of 8/1 or worse, expect displacement boats to be 13/1 or better. Naturally the hull forms are different too, but thats a quick ready reckoner if data or time is short.

In the lengths Im considering a displacement boat can manage 8 knots on 6HP, for a modern diesel that might have an output 5x that this is just sipping fuel at a litre an hour, more or less.

So what are the advantages?
You can be on the rhumb line course pretty much all the time, and the range is extended because you choose to cruise at 8 knots, perhaps to thousands of sea miles. Diesels are not known to be subject to 'overuse', and unlike rigging they have a servicing schedule instead of an onboard parts list. They dont require as much skill to sail, and pretty much anyone can crew a boat to some satisfaction. You wont run out of power for refrigeration or watermaker, and your lights will burn bright all night.

I understand the love of sail on the sea, clearly these boats arent going to ascend to that level of appeal, theyre just about efficient cruising.

[fuentes]

45 ft. Leopard. Loaded down with diesel generator, batteries, dive tanks and compressor, water, fuel, etc. 52 HP Yanmars, 1 engine, 1,800 RPM, in calm water around 5 knots. Both engines 1,800 RPM, 7 ft. swells, 26 knot winds against us 0.4 knots.

[Roy M]

Catsketcher, sorry to burst your bubble, but mine is not the only 40 to do twenty knots. The trick is to keep them light and to keep them moving.

[rbrentp]

Just to pile on. I have a Prout Snowgoose with twin outboards. One is the XLong shaft Honda 15 and the other is a Yamaha 25 Long.

The honda pushes the boat at about 6 knts at 3700 rpm and a half gallon per hour. The Yamaha pushes at 6 knts at 3400 rpm at 3/4 gal per hour.

The honda is four blade and five inches deeper in the water. The Yama is 3 blade. Together they push to 8. The Yama might do better with an extension kit and four blades as it cavitates at about 3600 or any wave action.

Eventually I will sell the Yama for a second honda. For similar results I will burn less fuel.

[Cadence]

Originally Posted by Roy M

Catsketcher, sorry to burst your bubble, but mine is not the only 40 to do twenty knots. The trick is to keep them light and to keep them moving.

Roy M, My 31SR had done 17.5 under sail and 7.5 was hull speed under power. So I can believe 20 with a 40. I'm sure it was an ama out of the water?

[Kita]

How about a Gemini 105mc catamaran motor in flat water about 6.5 knots at a little less than a gal per hr I think. That seems to be hull speed unless you have current to help or slow you down.

[ZULU40]

Originally Posted by Kita

How about a Gemini 105mc catamaran motor in flat water about 6.5 knots at a little less than a gal per hr I think. That seems to be hull speed unless you have current to help or slow you down.

Well ok but, hard to say for certain but its usual for suitable engines to be geared down to 2 or 2.5 to 1, and multi blade props. Four blades is usual, five is an experiment. So slow revolutions and maximise the grip, engine will need blowing out every few hours.

.

[Cherod]

Fwiiw. 36' x 20' , 2 x 8 hp ( yanmar ,direct shaft ) can do easy 6.5 knots x 1 ltr per hour , fantastic machine

[Cadence]

Originally Posted by ZULU40

Well ok but, hard to say for certain but its usual for suitable engines to be geared down to 2 or 2.5 to 1, and multi blade props. Four blades is usual, five is an experiment. So slow revolutions and maximise the grip, engine will need blowing out every few hours.

.

What?

[44'cruisingcat]

A member of this forum has fitted a Yamaha 60 high thrust to a Snell Easy. I think he could get speeds of around 12 - 14 knots out of it. Hopefully he'll jump in.

[Kita]

Originally Posted by ZULU40

Well ok but, hard to say for certain but its usual for suitable engines to be geared down to 2 or 2.5 to 1, and multi blade props. Four blades is usual, five is an experiment. So slow revolutions and maximise the grip, engine will need blowing out every few hours.

.

That is with the westerbeke diesel engine not the outboard version

[freeredcaz]

49ft Privilege, 2 yanmar engines - 7.5 knots both engines running. up to 12 with sails up.

[freeredcaz]

31ft Tri, Searunner, 9.9hp Toshimna petrol. 4-5 knots, much more with sails