Jet drive?

[Danielsan]

Hi there,

I would like to know if someone can recommend the use of a jet drive unit
as for ex. an Hamilton 274. What could be the pro's and contras for that type of drive?

All hints are welcome.

Greetz,

Daniel Peeters

What kind of design? Planning cabin cruiser, LOA7.40, LWL?6.10, BEAM 2.8,
displ. 2.5 tons. 1x 300HP engine (all metric dims.)

[Eric W. Sponberg]

From what I have seen, the Hamilton's seem to have the best reputation, and they have been most helpful to me in spec-ing a jet unit. If you have a single engine and jet, you have to be careful of the hull shape in front of the jet unit. Hamilton has some guidelines if you can talk to a Hamilton tech rep. They also have size selection charts to match the pump to the engine.

Eric

[Danielsan]

Thx Mr Spoonberg,

I already passed that stage and trying to design, (build) the hull according their specs. The only thing I was told by them was to use a constant deadrise between 5 and 25deg. I think at the moment I am at 22deg, for about 2/3 of the LOA. That is the only thing I did so far.

I somehow more like the principle of working of a jet drive. It seems to me that there are less stressed components than with other drive syst (exept direct drive through hull). Am I right with that?

But I have no idea about performance. (there are also many other things I don't know,...)

Greetings,

Daniel Peeters

Call them back, and they will tell you if the foward thrust is on the transom, OR the bottom mounted suction grate assembly.Do not guess. You can rip the boat apart, if you guess wrong.---------- As I recall, you will also need to build in a flat pad flush with the keel. Again, ask. Ask for a installation packet so you know what is really needed. Transom angle is also required. Just different.

[Morgig]

Don't forget the transverse loadings on the transom, these can be quite high. I know they have data for the larger jets (541 etc) so shold have the thrust data for these small ones.

300 hp was approved by them as enough for 9,000# of deep V? + added gear of a cruiser? 40' long ? I very much doubt it will get on plane with people, food , drinks, anchors, lines, fuel and maybe some canvas. Deep V's eat hp. Jet drives eat some more at all but the designed impeller rpm. I very strongly suggest you send them a copy of engine specifications and the boat plans before going any further. What speeds were you expecting with loads of people? I can see 1,500# easy added to the boat.

Average planing hulls with a 30:1 ratio do about 32 mph. A 40' deep V is not the average planing hull. There is another guy on this site having a problem with Hamilton Jet in his boat performing. I will look it up.

His post is 15 topics down this subject page.--jets/engine/deep V hulls. Read it and get in touch with him first. Good luck to both of you.

[hmattos]

If you want a good website to tell you about the pros and cons of a Hamilton HJ274 - then try the Hamilton site - hamjet.co.nz.

Regards
Hugh Mattos
C.Eng. M.I.Mech.E.
Technical Manager
Explorer Marine
www.explorermarine.co.uk