Propping down a Mariner 15 2 stroke for load

Simon Guest · 17 February 2006, 20:25

Well, following the discussion in the other thread I'm now ready to think about the prop to use with my Mariner 15hp 2 stroke and Zodiac Mk2C.

I currently have the standard 9 inch pitch prop supplied with the engine. This gives me scary amounts of speed with just me on board, and more comfortable amounts of speed with 2 adults and a child. However, with my intended load of 2 adults and 3 children it won't get onto the plane.

It appears that the basic aluminium props for Mariner 15 2 strokes are available in 8, 9, and 10 inch pitch. So how much extra load carrying capacity is moving to an 8 inch pitch going to give me? Can I go even lower? I guess I want to carry around 50kg more than I can get planing with so far, which for reference is about:

Boat: 50kg
Engine: 35kg
Fuel and misc stuff: 25kg?
Passengers: 200kg

I know that I can't reasonably carry around a 25hp engine, so I have to solve the problem by propping down the 15hp. I have seen guidelines that state an inch of pitch will increase my engine revs by around 100-150rpm, but what does that equate to in terms of extra load?

cheers,
Simon

Simon Guest · 19 February 2006, 21:04

Well, despite the silence here, an answer is revealing itself ...

I wanted to avoid an expensive guessing game, where I buy a series of replacement props, firstly 8 inch pitch, then 7 inch, and so on, hence my question.

But when I spoke to the dealer who supplied the boat and engine, he said simply send back the original 9 inch prop, and he'll send me an 8 inch. Yay! So here's a plug for P.A.Lynch (The Captain's Locker) in Morpeth, Northumberland, a dealer providing excellent after sales service.

cheers,
Simon

Poly · 19 February 2006, 21:32

do you thin he'll take mine back its got some big "dings" in it

codprawn · 19 February 2006, 22:32

Have you tried moving people forward until you get on the plane then moving further back?

My Quicksilver 310 with a suzuki 15hp 4stroke will plane with 3 adults and 2 kids on board - but only if someone leans right over the bow!!!

Simon Guest · 20 February 2006, 18:30

Quote:

Originally Posted by codprawn

Have you tried moving people forward until you get on the plane then moving further back?

My Quicksilver 310 with a suzuki 15hp 4stroke will plane with 3 adults and 2 kids on board - but only if someone leans right over the bow!!!

Not tried anything quite so extreme, but yes, I did make everyone hunch up at the front. Not enough with my 9" pitch prop, though.

What prop are you using?

cheers,
Simon

floater · 28 February 2006, 20:57

Hi hope you have fun, i used to run a zodiac fastroller 340dl with a yamaha 15 2 stroke,planed 4 up maxed out at 32 mph (1 up seats out bare boat sat on floor!) best fun i have had in years wave was jumpin of the northwales coast in 8ft breakers even had it on its transom in a howly best investment i had with my yam was to fit the hydroplanes on to the cavitation plate , yes it slowed it down but it planed instantly and was far more stable in a swell and at speed

hope this helps

Andy

Simon Guest · 13 March 2006, 21:54

Well, since the dealer swapped the original 9" pitch prop for an 8", we had a sunny day on Saturday out at Lymington, tried the new prop, and it worked a treat, what a huge difference from the 9" pitch. Now we have 2 adults and 3 children in the 3.8m Zodiac, planing easily.

Chuffed to bits with the new little SIB, and what performance from a 15hp - I'm impressed.

cheers,
Simon

ian parkes · 14 March 2006, 01:15

What gives here , you guys are finding you need wieght forward to get planing and Iam finding i need it back .

I had about 300kg in the boat , way too much fuel 35 litres ,
With one adult up front it planed ok but plowed and was a wet ride ,
Moved the adult back in middle with Kid in bow and it almost leaps onto the plane and stays there easily as I back off to about 1/2 throttle . My hull is a different shape to the quicksilver boats so maybe thats the reason , I guess my honda 4 stroke is heavier than the 15 mariner at 46kg but that should mean more wieght in the bow .

Searider · 14 March 2006, 09:31

Quote:

Originally Posted by ian parkes

What gives here , you guys are finding you need wieght forward to get planing and Iam finding i need it back .

I had about 300kg in the boat , way too much fuel 35 litres ,
With one adult up front it planed ok but plowed and was a wet ride ,
Moved the adult back in middle with Kid in bow and it almost leaps onto the plane and stays there easily as I back off to about 1/2 throttle . My hull is a different shape to the quicksilver boats so maybe thats the reason , I guess my honda 4 stroke is heavier than the 15 mariner at 46kg but that should mean more wieght in the bow .

Sounds like you might have the trim set too far in - the line of the propeller is pointing upwards, lifting the stern which will help with planing but drives the bow down once up to speed.

Try moving the tilt pin backwards a bit and see what happens.

Also make sure the boat is hard.