JETS

alain · 20 May 2001, 16:01

I was told recently by a manufacturer that jets compromise on the deep vee of the hull, which I assume means that they compromise the boats capability in rough weather.

Anyone has a different opinion?

I didnt know that jet powered boats do worst in heavy weather than outdrives .

Alan · 20 May 2001, 22:29

The problem with a jet drive in rough weather, as I understand it, is that if and when the boat gets sufficiently airborne to take the jet intake out of the water you lose all thrust. Whereas if a prop comes out of the water momentarily in doesn't have such a pronounced effect. I believe it is more difficult to maintain speed in a jet boat in the rough than with a prop. You are also not able to trim up or down with a jet wheras you can with a prop/outdrive leg.

This is all received wisdom rather than personal experience but I hope it helps!

Alan

tsunami · 21 May 2001, 15:52

After talking to Hamilton Jet and also Ocean Dynamics who operate most of their boats with jets they would have you believe that the boats are much better in the rough water than conventional prop boats!!
Apparently this is due to the fact that by dropping the bucket slightly it creates a suction effect and doesn't allow the boat to leave the water. The MOD are also testing Jet driven boats at the moment and have found that there exixting boats with props are left behind in rough condition, while the jet boats seem to get better in these conditions????
Has to be worth having a look at. I'm considering fitting a jet to my next boat.

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Joe

eksrae · 21 May 2001, 18:47

I would tend to disagree with jet boats being better in the rough water. here in canada jets are used in the river where shallower depths occur and it doesn't get so rough. i would hate to be in a jet in 3 metre seas. i could see it pounding hard do to the dead rise. The cost is way more than outboards as well. I know of a search and rescue boat that was lost killing three members do to lack of manouverability in the surf as well. A jet pump in our waters would plug up do to the debris in the water.

alain · 21 May 2001, 23:57

I am considering a jet too and until recently I was quite enthusiastic about it.

Now I am more and more conserned with the problems of reduced dead rise or the possibility of a choked water intake, plugged due to bottom debris or even sand.

After all, swallow water operation is what attracts most people to Jets.

It would be interesting to hear from commercial operators.

Powerboat · 23 May 2001, 21:38

Having driven several large Jet Boats I must say that I am still unconvinced .

Low speed handling is like Guinness ( an acquired taste ! ) The fancy tricks (Sideways waltzing and stopping in own lenght from 40 knots )that the salesmen show you will rarely if ever be needed in real life and you lose 30% of your engine power output through the jets .

Their only real advantage is that you have no prop to foul if operating in rocky or dodgy areas ( Which I often do in my real job )

We have had a few over here on trial or demo recently . One enthusiastic sales man ignored my advice to take it easy around the harbour with the Jet RIB (I was worried about wash etc ) .

This Chappie opened her up in the middle of Hodson Bay Harbour in about 2 meters of water and promptly hoovered a half ton of harbour mud through his intakes .

Result ........ Boat stops !!! and didn't go for about another hour despite having a Back Flush Feature !

Best wishes

Stuart www.powerboat.org

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www.powerboat.org

Charles · 23 May 2001, 22:08

I was fascinated by the Pulse Drive system displayed at Ribex. I was also pleased to meet the dealer,Lester Pallot, based in Jersey, Channel Islands. It would be well worth your while investigating this ... see also www.pulsedrive.net

Scubakid · 24 May 2001, 13:06

I have just sold a jet powered BWM 21 and the slow handling once you understand the change from prop is superb, I would agree that in the rough they loose power as the intake leaves the water and can slam a bit, you also need a lot of engine power. I have had to hang over the back/get in, to clear clogged intake many times if you use too much power in shallow depth it will suck the weeds up rocks and all and attach them to your intake like glue. That said I did like the boat and had some great fun in her.