Twin 580's in a speedster? Seeking better economy

[IDoSeaDoo]

Last weekend, I rode my buddy's twin 720 speedster and it changed my life! I now realize the downfall of the single engine challenger: lack of thrust! The 720 twins are loads of fun, but DAMN they are thirsty!!! 18GPH? That really hurts with today's fuel prices. I was thinking: what if instead of the 720's, you put in twin 580's? They only burn 5.5gph each AT WIDE OPEN! With about 55hp each, they should have the same total output as the 787, BUT the boat will have twice the pumps and twice the thrust. They are also much simpler and require way less maintenance than the beast 787. If the boat gets up to the same top speed as the challenger, I think I'll be content, but pulling skiers, tubers, and cornering I believe will be MUCH improved. What do you guys think?

 

[IDoSeaDoo]

BTW the 787 burns 11GPH at full throttle. The two 580's should have the same consumption rate at WOT, but be able to get more mpg at cruise as there will be twice the thrust. And do I need to mention the obvious benefit of NOT EVER GETTING STRANDED if a motor blows? I've had that displeasure all too recently and never want to go through it again!

 

[Guest_User]

seadoo would have built it if it were doo-able...
I`d say it stands to reason that the smaller engines would work harder and possibly need to have more throttle to maintain speed, and just might result in burning more or just as much as the 787. and I`d bet a smaller impeller to get the boat on plane resulting in more rpm and less speed.
jet boats are not efficient by any means, install 2 strokes in jet boats and they are the poster child for guzzling fuel...

you also need to be prepared with twin engine boats, yes if a motor goes down you have the opposite engine to bring you into port, but at idle to 2500 rpm speed, you will not get on plane and cruise home as you normally would under the power of both engines. and idling home against the current could take hours... remember to clamp the inlet water hose if going over 15 mph or when being towed in...

 

[Dr Honda]

If running right... the single 800 will pull a skier, and put a huge grin on your face.

Also... unlike a PWC... you won't hold it wide open very often... or for long distances. In a boat... if you are going for a destination ride... pull it back to about 75% power. You will only drop about 10~15 MPH, but cut the fuel consumption by about 35~40%


And finally... if you want to own a fuel powered toy... stop thinking about operating costs. Otherwise you won't enjoy it. My MONSTER Islandia holds 50 gal of fuel and gets a max of 2.5 MPG. At full throttle, it's at 0.78 mpg !!!! Sound bad, I know... but the reality is... I can go out for an entire weekend on a tank of fuel. When I went on vacation at Deep Creek MD last year... I think we only burnt half a tank over a 4 day trip. I do more "Anchor, and swim" days, over, "Driving around" days because of the price of fuel. Regardless... I'm out on the water, enjoying the day.

 

[IDoSeaDoo]

Still want to try it

Yea, you guys may be right on the engines working harder... And I know 2-strokes are gas-hogs It's unfortunate that SeaDoo didn't put the 155 4-tec into the speedster style boat. I dislike the new sportster body style and seating configuration that they went with for their lightest 4-tec boat. Unfortunately, even that boat is too heavy for my car to pull. I barely get away towing the 787 Challenger. Does anyone know what those galvanized trailers weigh? Maybe I can opt for an aluminum one... Don't get me wrong, the 787 Challenger has put many a smile on my face, despite the cavitation. I've ordered everything I can to fix that problem. Here's a question: if the impeller has a 2mm gouge that I smoothed out with a dremel, would that still make it cavitate? It's a nice, aftertmarket Swirl prop, but the PO obviously enjoyed his time in the rocky shallows with it. Also, on aftermarket wear rings without the OEM lip, should I put one in with said dremel?