Will a 10hp motor get my Yam 340S onto the plane?

[lightning]

Would you hold the engine at WOT for long periods anyway?

My boat will do 19mph at WOT (5500rpm with my setup) However it is less noisy and generally feels better backed off a bit to about 5000 rpm (after using full throttle to get up to speed if required) which still gives 17mph, the difference in speed being hardly noticeable.

[Max...]

Originally Posted by lightning

Would you hold the engine at WOT for long periods anyway?

My boat will do 19mph at WOT (5500rpm with my setup) However it is less noisy and generally feels better backed off a bit to about 5000 rpm (after using full throttle to get up to speed if required) which still gives 17mph, the difference in speed being hardly noticeable.

+1 Same here, 3.4m with 9.8 Twat does 17.5 kts flat out at 5540 rpm. I usually run at 15 or so.

Not sure if Loco's working in US gallons but its often quoted in the UK as 10% of HP at WOT in gallons per hour so 4.5 litres per hour for the Twat which seems to tally with users figures.

Your Mariner at double that sounds none too healthy...

[sergeant]

My 3.8m with a 15HP 2str easily gets onto the plane with 2 adults onboard.

[lightning]

I used about 15 litres of fuel in Scotland last month on my SIB with my Tohatsu 9.8.

This equated to ten hours on the water according to the hour meter on my TinyTach.
Speeds were varied, some trolling some medium speeds and some at full power. Mostly with two of us on board.

With this engine the SIB planes effortlessly without having to shift our position or anything, although my wife sits near the front anyway.

I changed the prop for my spare which is a 9.5 pitch and the boat still planed, although there was a slight delay while it got "out of the hole" and the RPM maxed at 5,000.
Top speed was the same! 19mph

The engine actually sounded better with this prop as RPM for a given speed was lower (RPM at 10mph 2800/3200 for instance)
Also when trolling it was smoother, I assume due to increased load on the engine?
But I was advised not to use it and to go back to the 8.5 pitch as it was "straining" the engine.

[IanH]

Originally Posted by neil9327

I think I was a bit unlucky with the current one. I had tied my boat up on a disused dredging boat on the Basingstoke canal near Aldershot (UK) specifically to keep it away and partially hidden from a car park adjacent to the public slipway there. I was only gone 2 hours during twilight while I returned to Winchfield to collect my car. The thief had to jump a 80cm gap between the dredging boat and the canal bank carrying the motor at the same time - must have been more athletic than me!
And they had it away with a 3/4 full 50-litre fuel tank too.
I reported it to the police. But I can't expect them to find anything.

I would hope for your sake they don't notify the canal authorities of your loss. Basingstoke canal has a rigorously enforced max HP rating at 2.5hp/m. For your 3.4m boat, that makes the max for your boat 8.5HP. I also guess you were not registered either as they flatly refused to register my boat that was, depending on how you look at it, 36cm too short or 0.9HP over powered even though I suggested modifying the boat to meet the regulations.