Big runabout with jet propulsion?

About using jet ski motors to power small boats

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mike_57
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Joined: Tue Sep 08, 2020 5:06 pm

Big runabout with jet propulsion?

Post by mike_57 »

So I searched every page of this section of the forum and I did not see anyone out there using jet propulsion in any of the big runabouts. I'm really curious about running twin jets from a Sea-doo or Yamaha boat in a Riviera, Tahoe, or Monte Carlo.
These three designs seem to have enough of a vee in the hull to work with jet drives, I'm still trying to do research on all of this but I thought I'd ask to see if I'm missing something glaringly obvious.
Would the weight of the engines/drives in the rear of the boat be too great?
I don't think hp would be an issue as I wouldn't plan on anything less than 150hp per engine in a smaller Riviera or Tahoe and at least 200hp per engine for the bigger designs.

Let me hear some thoughts!

JimmY
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Re: Big runabout with jet propulsion?

Post by JimmY »

Any of the inboards are designed to have the engine weight more forward in the boat. These designs have narrower sterns and will not sit right in the water with more weight in the stern. You need to look at boat designs for an outboard or I/O drive. This is why you won't see any builds of these boats with that kind of power.

Do you have some requirements for the jet drives? Like shallow lake or river? From the 2 data points I have on Yamaha twin boats, they suck gas, suck up tow ropes, have no directional control at slow speed or when crossing wakes, and sound like a hive of bees. The 2 people I know with them are not thrilled with them.
-Jim
Nothing says poor craftsmanship like wrinkles in your duct tape!

mike_57
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Re: Big runabout with jet propulsion?

Post by mike_57 »

JimmY wrote:
Sun Sep 13, 2020 11:48 am
Any of the inboards are designed to have the engine weight more forward in the boat. These designs have narrower sterns and will not sit right in the water with more weight in the stern. You need to look at boat designs for an outboard or I/O drive. This is why you won't see any builds of these boats with that kind of power.

Do you have some requirements for the jet drives? Like shallow lake or river? From the 2 data points I have on Yamaha twin boats, they suck gas, suck up tow ropes, have no directional control at slow speed or when crossing wakes, and sound like a hive of bees. The 2 people I know with them are not thrilled with them.
That's what I had thought but didn't want to believe honestly.. I had hoped that with the lighter engines it could still be done. I've flipped through the other options I could convert to jets and they just don't flip the switch like these bigger mahogany designs do.

I currently own a Speedster 200 and that's where my bias comes from. Low speed you do tend to be making a lot of small adjustments for sure, and if you get a rope under the boat it'll probably end your day at the lake unless you have tools. But I tend to find it to be reasonable on gas and a riot to drive.

TAB
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Location: OR

Re: Big runabout with jet propulsion?

Post by TAB »

Something else to think about is fuel burn. 2 jet ski motors will burn about a 50 %more fuel then a simlar displaced inboard.

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Roberta
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Re: Big runabout with jet propulsion?

Post by Roberta »

You might look at boats like the Rampage that have used Berkeley jet pumps and similarly modify the bottom of a more classic design. The engine could be placed in the normal location with a shaft to the pump.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

mike_57
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Joined: Tue Sep 08, 2020 5:06 pm

Re: Big runabout with jet propulsion?

Post by mike_57 »

Roberta wrote:
Thu Sep 17, 2020 2:11 pm
You might look at boats like the Rampage that have used Berkeley jet pumps and similarly modify the bottom of a more classic design. The engine could be placed in the normal location with a shaft to the pump.

Roberta
Unfortunately I don't have the confidence to modify a hull design to suit this.
However I have been looking through all of the other designs that I can take a look at and it seems like the Roustabout may be a good option for what I'm looking to do.

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