Fantasy Rib time!

Simon B · 27 July 2010, 15:36

OK Chaps, what's the best diesel engine to buy to couple up to a hamilton waterjet in my fantasy 6.8-7.8 build?

Cummins mentioned by Andre looks good.

MarkWildey · 27 July 2010, 16:31

SeaTek bi-turbo or maybe a FPT

RIBRyda · 27 July 2010, 18:30

Not getting into specific makes, models or types - just bear in mind that even as a dream boat you'd need to allow at least 50% more power for a jet unit than for a comparable conventional prop unit; last time we did the sums we decided to bin the idea quickly on cost and economy grounds. IMHO of course!

GJ0KYZ · 27 July 2010, 19:40

That's an interesting question; I think my next boat will have a jet drive since I'm only really interested in skinny water cruising nowadays. Ribcraft recommend a Hamilton HJ322 water jet drive, ZF Marine 280 1:1 direct mounted marine transmission, Centa GZ double element coupling drive shaft and Caterpillar 3126 7.2 litre diesel for their 10.5m boat (£98K all in). I don't know what they'd suggest for a smaller rib.

Thing is, if you only want a jet drive for shallow water it may pay to look at craft other than ribs. For instance SeaDoo have a 23' runabout aimed at the US market but which is available through UK dealers. It looks ghey and you probably have to be a trustafarian to own one but it's powered by two 215hp Rotax 4-stroke supercharged direct drive jets resulting in 55kts WOT and - check this - a draft of only 12 inches! I could get to M.St.M on neaps with that kind of baby. Lush.

http://www.sea-doo.com/en/sportboat/...challenger230/

willk · 27 July 2010, 20:36

Quote:

Originally Posted by GJ0KYZ

check this - a draft of only 12 inches! I could get to M.St.M on neaps with that kind of baby.

Yes, but ze inhabitants, zay vood fart in your general directionne and suggest that your fazzer smelled of elderberries.

"Ghey" - I am amused

Mollers · 27 July 2010, 21:01

Jet drive- The best way to turn horsepower into bubbles without all that unecessary propulsion.

GJ0KYZ · 27 July 2010, 21:12

Quote:

Originally Posted by Mollers

Jet drive- The best way to turn horsepower into bubbles without all that unecessary propulsion.

err... have you seen the accelaration figures for jetskis like the SeaDoo RPX-X? 0-50mph in under three seconds. Check this out:

http://www.youtube.com/watch?v=_bZ6H08-tpY

GJ0KYZ · 27 July 2010, 21:20

Quote:

Originally Posted by willk

Yes, but ze inhabitants, zay vood fart in your general directionne and suggest that your fazzer smelled of elderberries.

That's a bit of a negative attitude you have toward the French there Willk. The French ribbers who visit this site have probably have never heard of MPFC. Personally I've always found the French to be extremely courteous sailors.

willk · 27 July 2010, 21:36

Quote:

Originally Posted by GJ0KYZ

That's a bit of a negative attitude you have toward the French there Willk.

Not at all, but as a Foreigner on this site, I say the French are well able to look after themselves and we must all paddle/pole* our own rib, draft permitting.

I've always found the French to be dead on (I employ 3), once they knew that I wasn't English...

_____________
*Poles are another matter

Simon B · 27 July 2010, 21:43

Quote:

Originally Posted by RIBRyda

Not getting into specific makes, models or types - just bear in mind that even as a dream boat you'd need to allow at least 50% more power for a jet unit than for a comparable conventional prop unit; last time we did the sums we decided to bin the idea quickly on cost and economy grounds. IMHO of course!

Strewth, I thought it was 33% that Cameron has much to answer for in terms of inflation!

The jet idea was to reduce possibility of prop strike on divers in water. Not to bothered about acceleration but economy could be a factor.

Keep the ideas coming, it's the only way I'll learn!

GJ0KYZ · 27 July 2010, 21:48

Quote:

Originally Posted by Simon B

Strewth, I thought it was 33% that Cameron has much to answer for in terms of inflation!

I think it is around 33% - that's what Ribcraft said, as did the engineers who look after my outboard.

MarkWildey · 27 July 2010, 23:24

Quote:

Originally Posted by Simon B

The jet idea was to reduce possibility of prop strike on divers in water. Not to bothered about acceleration but economy could be a factor.

I'll need to be careful how I say this.... Instead of cutting them up you can suck them into the intake!

RIBRyda · 28 July 2010, 07:38

Percentages, Schmentages!

Somewhere between 33% and 50%, depending on engine, gearbox, powertrain loss factor, etc etc.... The main cause of inefficiency is that the rev range on the jet unit usually doesn't marry at all well with the output from the engine so you need an inefficient gearbox with all those heavy whirly bits in to create the right bubble factor at the back end.

biffer · 28 July 2010, 07:55

you need the biggest engine you can get into the boat, you then get into a weight problems, i'm thinking a yanmar 320hp, but unless you're going to put it under the console it's going to take half you're boat up, the cummins are good lumps but they are heavy, a lot of organisations (police, fire etc) use styer engines. they can be difficult to maintain without specialist tools

martini · 04 August 2010, 15:00

Quote:

Originally Posted by GJ0KYZ

That's an interesting question; I think my next boat will have a jet drive since I'm only really interested in skinny water cruising nowadays.

Reckon I could build you a nice aluminium hulled jet drive rib, ever better for exploring puddles

Quote:

Originally Posted by GJ0KYZ

Ribcraft recommend a Hamilton HJ322 water jet drive, ZF Marine 280 1:1 direct mounted marine transmission, Centa GZ double element coupling drive shaft and Caterpillar 3126 7.2 litre diesel for their 10.5m boat (£98K all in). I don't know what they'd suggest for a smaller rib.

Would like to think I could do it for less than £98k as well