A co-worker is considering a new jetcraft 18' sled, dry weight without people and fuel is 947 LBS I think. She said they were looking to get it with a 90 horse outboard jet. Opinions??? Enough ponies or not enough.
I love an excuse to do a little math. Shows the kids that it may be useful to pay attention in class. :smile:
I'm assuming that weight listed above is sans kicker, basically the outfitted hull, with the big motor.
My boat is 19 ft, 1450 dry weight, before kicker, etc. I estimate weight with kicker, fuel, accesories is about 1900 lbs. I get good performance out of a Merc Sportjet at 175 hp. I believe the Sportjet is rated at 175 hp delivered, as opposed to powerhead HP. That implies a horsepower to weight ratio of 10.8 lbs per hp. I had a 17 ft sled some years back, with an 85hp on it, or about 59.5 delivered. It had a total working weight of about 1300 lbs. that works out to 21.8 lbs per horse power. That boat was very difficult to plane with 3 people on it. So somewhere between 22 lbs per hp and 10 lbs per hp is where you want to be.
If your friend's boat is 1000 lbs WITH MOTOR, I'd add back in the weight of kicker, fuel, and some stuff, same as I did above. Call it 400 lbs. Now we have 1400 lbs before people and gear. The range implied by those numbers is 63 hp delivered to 140 hp delivered, or (surprise) 90 hp powerhead to 200 hp powerhead.
Now, my boat is a hot rod, and you don't need to go that fast. But if you don't have sufficient power, you won't be safe or comfortable running white water, in which case, why get a pump? I suspect 90 hp would below that minimum. That would be the same as on my old sled, and it was too little for me to feel comfortable on the clack with 3 people in the boat.
So, yeah, I'd tell your friend, seems a bit light.
I had a 19' Jetcraft with a windshield, 50 gal tank, 9.9 four stroke kicker. A 200 Yamaha jet with a 4 blade impeller pushed it just fine, great hole shot. I would not have wanted any less than 150 hp.