Jet Drive Opinions wanted

[hsagman]

Hi all. I'm looking at boats with Jet Drives (i.e. Little Harbor 34). Any opinions? I know nothing about jet drives. Always had good old props. Thanks in advance.

[RaymondR]

They tend to have a reputation for high fuel consumption, don't know how deserved it is having never owned or operated one.

[rbk]

General rule is 40% reduced efficiency with a jet vs prop. Depending on the hull & inboard/outboard you will also notice significant slippage in the back end when turning hard and may even skip and start sucking air. Most don’t like anything more than a slight chop more so when you have a complimenting hull (flat).

[Cheechako]

I have some experience in testing and installing jet drives. I like them in some ways. Great for shallow water work but will suck gravel off the riverbed! They are inefficient compared with props. Seems some sort of jet drive would be cool for sailboats if the details could be worked out regarding the intake somehow.

We put many jet drives in aluminum V hulls and had no issues.
They are super maneuverable once you get it down.

We built about twenty five 23 foot boats each with two big Cummins 6 cyl diesels and jet drives.

[captmikem]

I had a Novurania tender around 24 ft. with a yanmar diesel and a Hamilton Jet drive.

It was a good tender, it took a bit to get used to the jet drive but once you figure it out it is very maneuverable. I could come into a slip and rotate it within its own length at half throttle quickly or very slowly. Coming alongside was just flat easy. Using the bucket to control speed instead of the throttle kept the maneuverability up, and you could come into reverse at full throttle and stop just like that, or you could be very gentle and smooth.

It was a bit slow on the takeoff, pulling two skiers out of the water was a bit boggy but possible.

Up in the ice it was a great boat as it would flow right over bits of ice in the water without worrying about prop damage.

I lost bucket control once up in the Aleutians far away from the ship, so no steering. But I found once on a plane I could move side to side to steer and made it several miles back to the ship.

I had few complaints with it.

M

[BruceS]

In a big following sea or big swell you get the see the stern of your boat quite often.
Chap had a twin in a 36ft boat & soon parked it rather than go around his lobster pots in lumpy water. (reefs/swell/seas)
For info it was the dive boat that "left a couple of divers behind" off Qld coast in previous life.
https://en.wikipedia.org/wiki/Disapp...ileen_Lonergan

[KP44]

If your style of sailing is to use the sails most of the time, a jet might give the advantage of no prop drag much like a good folding prop.
The last I heard, jet drives are about 40% effecient so if you motor even part time you will use a lot of fuel compared to a conventional drive. (Not 40% less, but 40%. Which is 60% less efficient.)
I have no experience except in a small open boats used to move logs.

[billgewater]

Had an experience some years ago on a 50 ft twin hulled motor vessel with jet drives. Inefficient mainly, but they were also unstable when motoring . The problem was that if the boat veered slightly to port then the boat would accelerate to port. i.e. it was really directionally unstable. It was really difficult to steer in a straight line. The jet drives were removed and conventional drives installed (at considerable expense). Faster, more efficient, directionally stable.
Jet drives were developed in NZ for shallow river tourism and appeared in the large wave piercing high speed catamarans that evolved in Tasmania and Western Aus. Jet drives are used on some of the Thames London high speed ferries. They are a specialist product and you should be talking to someone with considerable expertise in the area.

[Mlp48]

Some time ago, I was asked to go for a ride on jet drive boat and in Maine and the owner/driver blasted through a thick field of lobster pots as if they were not there. That's the great beauty of them !

There's nothing outside to foul. There is a prop involved but it is inside and encased. However, that and the wear ring and cathodic "zincs" will need attention if the boat is left in the water and not in a lift.

They will go in shallow water BUT will not work in water so shallow that they can't pick it up water to propel !

There could be power lost to the jet process but I've also been aboard two similarly sized boats, one jet and one prop, and each with a same brand of 440 hp powerplant. I did not see a great difference.

A "manual bucket" boat or boat without computerized control will take some guided practice but it can be done and mastered. The "Jetstick" popularized Hinckley's offerings which would have otherwise been "manual bucket" boats. The Jetstick is genius but not without complications.

[Pete7]

Originally Posted by KP44

If your style of sailing is to use the sails most of the time, a jet might give the advantage of no prop drag much like a good folding prop.

The problem is often the loss of buoyancy at the stern by having a large hole for the intake, particularly if a hull designed for a shaft or stern drive was used rather than starting again. For a yacht that pick up could really add drag.

A previous dive boat was a 22ft rib with big 4.2L TD and commercial stern drive. This would top out at 29 knots in light trim. I was offered the chance to buy a sister rib which had been converted to jet drive. Top speed was 15 knots and at slow speed we spent most of our time going sideways or zig zagging. It was a laugh for half an hour, but no way was I buying that boat.

Pete

[johnn33]

You may be interested in these sites
https://www.international-maritime-r...member-profile
https://rnli.org/what-we-do/lifeboat...class-lifeboat
Much depends on your hull shape and engine efficiency figures.

John

[Tom in Florida]

I would no longer consider a jet drive engine. I made the big mistake of buying a 19-ft Yamaha at the Miami Boat Show a couple years ago. I had read a biased review in Boat/US Magazine, which was all positive and no negative on their jet drive. But the negatives are many: 1. Pump sucks up weeds, twigs, and other debris, making it necessary to stop and clean out the pump frequently; 2. Have to run up to almost 5,000 rpm to approach plane; 3. If you want to putt around at 5 mph, gas mileage is good, but if you want to get up to over 10 mph, gas mileage is lousy. 4. Have never exceeded 20 mph, engine not capable.


Tom

[rbk]

Originally Posted by Tom in Florida

I would no longer consider a jet drive engine. I made the big mistake of buying a 19-ft Yamaha at the Miami Boat Show a couple years ago. I had read a biased review in Boat/US Magazine, which was all positive and no negative on their jet drive. But the negatives are many: 1. Pump sucks up weeds, twigs, and other debris, making it necessary to stop and clean out the pump frequently; 2. Have to run up to almost 5,000 rpm to approach plane; 3. If you want to putt around at 5 mph, gas mileage is good, but if you want to get up to over 10 mph, gas mileage is lousy. 4. Have never exceeded 20 mph, engine not capable.


Tom

Not disagreeing with the negatives but it also sounds like the engine is undersized for the boat. I've had/have several and never had to max out to get on step unless overloaded (which is another negative =less capacity) and can usually cruise around on step easily between 50-75% throttle. You really have to remember that if you for instance get a 50Hp powerhead it will act like a 30Hp with the jet leg. A 50Hp prop on a 19' should be no problem but with a jet and a couple of people/gear you could bog out a 30Hp no problem. That said the outboard jet legs have the advantage of being able to carry the prop leg with you or vise versa and use the more efficient powerful prop for the heavy lifting then swap to the jet for exploring skinny areas (takes about an hour on big outboards) This has the advantage of carrying 40% less fuel as compared to running a straight jet. Also check your wear ring and impeller as I've seen clearances way to big and also the leading edge back filed with the wrong profile. Cavitation also kills the power on a jet.