Re: Jet boat for ocean
We have a small jetboat. It has an OB powerhead mounted on an inboard jetpump -- a very common brand and arrangement in the mid-90's when the boat was built.
Advantages / Disadvantages
(1) can go in much shallower water IF there's no weeds etc. BUT weeds in the pump intake will starve the engine; sand stirred up from the bottom can destroy the engine.
(2) At high speed, steering is excellent and immediate. BUT at low (no-wake) speed steering is problematic. Remember your steering is from the directed force of the jet, not a rudder or even a skeg under the prop. If you drift at all, you have absolutely nothing to maintain the attitude of the boat.
(3) There is no prop, so there is no danger of the prop cutting into someone. I suppose that's a bit of a safety factor, but you shouldn't have the motor running with anyone behind it anyway. That said, I usually start the engine and push the boat a little deeper before I hop in -- but that's more a function of being at a rather shallow lake. There really is no neutral. If the motor is running, there's at least some propulsion; even at idle, the jet pump has some water going trhough it (or you'd overheat the engine).
(4) If you get into weeds with a prop, many times you can put it into reverse and clear the weeds. With a jetboat, I've had to stop the engine, dive under the boat, and pull the weeds from the intake grate. I've heard there are some intake grates that can clear matted weeds but I've never seen one.
(5) My 13.5' jetboat has a 90 HP Merc SportJet engine (common in the mid-90's when it was built). I estimate it has the power and speed of about a 45-50 HP prop. Thus it's rather underpowered and I cannot get an adult up on a slalom ski -- two skis are ok. Tubing is ok, but not much the huge tubes I've bgun to see on our lake.
(6) My gas 'mileage' is not good. I've got a 16 gal tank. A few years ago we went on Michigan's Inland Waterway across the tip of the lower peninsula from Burt Lake to Cheboygan on Lake Huron. I figure the trip was about 30 - 35 miles with about half at slow no-wake speed. Slow speeds are very inefficient for us. It took me about 1.5 tanks (~24 gal) of fuel. We went with a friend of ours who has a newer and larger (16' SeaDoo) jetboat with the same size tank. He did the round trip on only 3/4 tank (~12 gal). So a newer motor and drive can make a huge difference.
Even with all these issues, the fun factor is tremendous. I've never done it, but there are plenty of you-tube videos of small jet boats doing a 180* high-speed turn, driving their bow into their wake and 'submarining'. The water self-drains, everyone's soaked, but a lot of people think it's lots of fun.
I've heard there are jet drive OB, but I've never seen them around here.
Since the intake water is used for both cooling and propulsion, recognize that you'll be pumping salt water through some pretty precision machinery. You'll need to be sure to rinse it in fresh water after each exposure to salt in order to minimize corrosion.
Sorry about the length of this. Hope it gives yoiu some things to ponder.
Al
