How fast,...

[Trevethan]

....Should a lightweight (two people can lift) fairly flatbottomed 11 foot "speedboat" go while driven by a 9 hp outboard?

An why does seem to rev higher and want to go faster in reverse?

prop is clean, orginal evinrude. No dings or chips.

Cheers,


Nick




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[JimMcMillan]

If its not a planing hull it wont matter if you have a 90hp engine on the back it will just dig its back end in and make big waves and will not exceed its potential speed. This will make the engine labour and not rev to its full potential,when going astern you are probably not reaching design speed so engine appears to be revving more easily.

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[Trevethan]

It does look like a planing hull though!

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[snowleopard]

should get 15-20 knots.

are you sure it doesn't just seem to be faster in reverse because it's more alarming?!

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[BrendanS]

might be the angle the outboard is set at. Is the bow rising, and stern digging in? If so, try putting more weight forward and seeing if that improves things - if it does, you can think about altering the angle of the outboard

<hr width=100% size=1>Me transmitte sursum, caledoni

 

[cameronke]

Could the engine be cavitating in reverse?

The first time I experienced cavitation I thought that I had lost my prop!

Regards
Cameron

<hr width=100% size=1>Work to live, live to sail

 

[Trevethan]

Made about 7 knots!

There seemed to be more thrust astern... but as you said, could be all that water sloshing against the transom etc......

Speed improved a bit with lots of weight forward, but only by a knot or two and only managed to plane for a few seconds when I caught another wake right.

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[snowleopard]

if it really is a planing hull form you have a radical problem. my dinghy planes with a 3.3hp motor!

the rake angle may be wrong causing the bow to rise, in which case alter the tilt so the prop is further forward.

if you can post a photo of the bottom of the boat the combined expertise on the site should be able to assess its potential.

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[BrendanS]

the only other thing I can think of, other than rake angle, is that it is overpropped? as well as photo of bottom of hull, a couple of photos of outboard in relation to hull from side and rear would help

other question that will hopefully be answered by photo, is the outboard short or long shaft?

<hr width=100% size=1>Me transmitte sursum, caledoni

 

[Trevethan]

Will try to post some pics if I can't sort the thing out this weekend. It's a twin cyl, shortshaft evinrude of early eighties vintage.

Thanks for all the help!

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[JimMcMillan]

are u towing a large sternwave

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