REPOWER to a Jet Drive!!!

[Kwasy Wabbit]

Hello All,

I am new on this site so appologise in advance if this question has been asked or if there is better forum to post it under...
I am looking to re-power my 92 Bayliner Capri (20') bowrider and change it into a jet drive powered boat.
The current engine will not do as it is setup for the dreaded Force L-Drive. I am looking for a whole new motor and of course, jet drive unit!

Can anyone suggest what a good choice of inboard motor and drive might be for this very ambitious project. Keeping in mind a good balance between power, and fuel economy. The boat has a gross weight of around 2000-2200 lbs.

 

[CDK]

If this quote from your post is meant seriously: "Keeping in mind a good balance between power, and fuel economy. " then immediately forget about your project.

Whatever reasons people have to install a jet drive, fuel economy isn't one of them.

 

[Kwasy Wabbit]

Ok. I took your advice,scrapped the project and sold the boat...
Anyhow... I will clarify, for those who need it, what I meant by a balance between fuel economy and power.
Any one can go the route of overkill and throw in a huge V8 and couple it with a drive unit. What I am looking for is 'advice' on the optimal motor and drive for this project. I joined this forum looking for real advice.

 

[baeckmo]

Check the Mercruiser jet + engine combinations. You get a complete kit, all pieces matching, ready to install from a well known brand with a world-wide service web.

 

[keysdisease]

Is there a compelling reason to choose jet over prop?

 

[Kwasy Wabbit]

Because jets are cool!!!:

 

[miamitech]

jet drive rocks

ok compelling reason for jet drive over prop, no missing limbs... you cant hurt a manatee with jet drive. you can go into shallower water, props get stolen, damaged. im about to jet drive a rib with a jetski motor. watch for the build up, i also plan a jetdrive sailboat.

 

[tom kane]

Jets are not good in shallow water they suck up the bottom rocks and mud and suck onto the sandy bottom with a sudden stop. Ruined impellers result. Just like props. They ingest weeds and plastic bags and ropes and anything going and stop or slow down so jump under your boat and try and clean rubbish out. You can not steer a jet unless you have power and that is no fun in some places. You have to go everywhere fast and that is no fun or pleasure at all. If you call 3 feet of water shallow ( the limit ) you will be OK and maybe you can skim over some shallows but if you stop in very shallow water you will not start again so get out and walk home. Your boat will need to have a reasonably deep V hull to prime and run easily. If you get caught in fast following seas your boat will probably constantly broach because it would be dangerous to speed. There is much more. Jets are fun for those that can afford to burn money and there are millions all over the world doing what they do best, but not in shallow water (10 inches).

 

[speedboats]

Jets are not good in shallow water they suck up the bottom rocks and mud and suck onto the sandy bottom with a sudden stop. Ruined impellers result. Just like props. They ingest weeds and plastic bags and ropes and anything going and stop or slow down so jump under your boat and try and clean rubbish out. You can not steer a jet unless you have power and that is no fun in some places. You have to go everywhere fast and that is no fun or pleasure at all. If you call 3 feet of water shallow ( the limit ) you will be OK and maybe you can skim over some shallows but if you stop in very shallow water you will not start again so get out and walk home. Your boat will need to have a reasonably deep V hull to prime and run easily. If you get caught in fast following seas your boat will probably constantly broach because it would be dangerous to speed. There is much more. Jets are fun for those that can afford to burn money and there are millions all over the world doing what they do best, but not in shallow water (10 inches).

Clearly mis-informed with limited jet experience, probably with jets in the '70's

 

[Red Right Return]

A good friend of mine got a whaler with a omc jet. They were taking day treks into small bays mostly very shallow. They would take their boat thru sandbars, rocks, etc and close enough to shore to leave it on a small anchor in knee deep water while they walked around for a few hours or had picnics. After two years they went back to outboard. The omc jet had too many problems sucking up things, etc.
Tilting up the outboard was less trouble.

 

[speedboats]

A good friend of mine got a whaler with a omc jet. They were taking day treks into small bays mostly very shallow. They would take their boat thru sandbars, rocks, etc and close enough to shore to leave it on a small anchor in knee deep water while they walked around for a few hours or had picnics. After two years they went back to outboard. The omc jet had too many problems sucking up things, etc.
Tilting up the outboard was less trouble.

Did OMC make a jet? Or was it one of those abortive and problematic (in my opinion) outboard versions? (simply bolt a jet onto an outboard leg and try to capture a new market, which again IMO did jets a rather large dis-service)

 

[Red Right Return]

Omc named it a turbo jet. It was a 115 hp powerhead mounted inside the boat.

 

[speedboats]

Ah yes, I do recall seeing a few now. They were about the same time as the Merc Sportjet came out. Nowhere near as successful, athough Merc did have the sense (in the end) to use much larger powerheads even if it was still only a 7.25" pump..

The problems with most problematic jet installs is the hull setup. In the '70's Hamilton Jet where starting their campaign "Born in the River to play in the Sea", unfortunately the pump design was playing catch-up as the same 7.5" multi-stage pumps that were used to propel light weight river boats were being used for much heavier sea-going vessels. This coupled with the lack of insight / knowledge in regard to hull shape for correct pump loading ment that alot of the early sea-going jetboats were nothing more than underpowered scalled up riverboats. This is where most get their impression that jets wander all over the place, won't go in a straight lins, won't pull skiiers etc.

With response to Tom Kane's comment

If you get caught in fast following seas your boat will probably constantly broach because it would be dangerous to speed.

Why would a vessel broach simply because it is propelled by a jet? Because it has a deep vee that was mentioned earlier? There are plenty of deep vee outboard and I/O powered vessels, are you saying that they are safer and don't need to go as fast simply due to the method of propulsion? That is simply rediculious. That is a function of hull design, and while allowances need to be made or considered when installing a jet, they are nowhere near the detriment you publish here.

While I will conceed that weed can be problematic with waterjets, weed grills can be installed if you are unlikely to pump gravel, otherwise I've driven over plenty of stuff without fear of sucking stuff off the bottom. I saw a youtube clip recently that was clearly produced for Mercury Stern-drives which claimed that the jet would suck sand and gravel from the bottom of the river / lake / sea from several feet away. I can assure you I have not experienced this and I've specialised in waterjets for the last 17 years. Yes plastic bags and floating weed can get stuck to the grill / grate when idling around off the plane, yes you do need to shut down and use a weed rake or rock the boat to remove it, but they can also wrap around the front of your outboard or I/O leg which will require you to do the same

 

[Mr Efficiency]

The sorts of speeds at which jets become efficient compared to propellor drives are quite high, and offshore too high for comfort in the typical trailerboat. This is why they have remained a specialty, rather than the main choice.

 

[tom kane]

Jet and surface drives and pod drives in a really bad following sea the stern rises with the oncoming following wave and forward drive is lost because the prop or impeller is to close to the surface.
All thrust is lost so your boat is certain to broach. If you could go faster than the following seas (which you can not reasonably do) the problem would be less. The same problem arises in twin installation craft in rough seas the boat rocks from side to side and the props loose thrust.
I have seen many pleasure jet driven craft on hard stands with all sorts of debris stuck in the intakes and new impeller being installed, it takes very little to impair the thrust.

Added image shows a blown jet. In jested to much sand and shingle.