First post - and of course it has to be about prop choice!

[Pat]

Nothing like the sort of boats or engines you boys are running, but you seem pretty shit-hot on the technical stuff and I'm new to it!
I have a Fletcher 13ft Arrowsport with a mid-80s Yamaha 50hp on the back. Existing prop is 11 1/4 x 14. Boat weighs about 250kg, engine about 80.
With one or two people on board it goes up on the plane well, and shifts fast enough once up there (fairly smooth lake). With one person on board it'll sometimes ventilate/cavitate for a second or two if I give it full throttle from a standing start, and then settle down and sit on the plane happily. Anti-Cavitation plates are about even with the bottom of the hull. A pair of Doel fins are on it.
The real problem comes when I have a heavy load on board, say 4 people (a tight squeeze!). The boat won't go up on the plane at all, it just ploughs through the water. No power t/t yet, though I have one ready to be fitted - it's currently set with the manual trim pin on the second hole out.
Now to the unexciting part. By happy coincidence I managed to clip one of those floating rocks the other weekend, so now I have to either pick up a new/recon prop or have the existing one repaired.
Any guesses as to my best bet, so that I can still get up on the plane 4-up, but not totally kill off my top speed with just me in it? Or is it simply the case that I don't have enough power altogether and it'll never plane under a heavy load? (although Fletcher quote a max of 40hp for the hull).

Open to any and all suggestions. I don't have a tach (one on the way from the states), and obviously there's no point taching it now with the beaten to death prop!

Apologies for the lengthy post, I just have no idea what sort of pitch/diameter prop would be my best bet!

Cheers,

Pat.

[Pat]

Oh, forgot to mention - existing prop is 3-blade ali, though you probably guessed that!

[FrenchPhil]

No 50hp won't be any good for 4 people no matter what prop you use

[Pat]

Cheers, looks like I'll be boarding off the back seats then!

[TheOrs]

Originally Posted by FrenchPhil

No 50hp won't be any good for 4 people no matter what prop you use

My old 15 footer (unknown make) would plane off with 4 up (just) using a 50HP Merc & that was pre-ICOMIA. I think it had a 13" pitch prop.

Pat; I'm a bit confused about your boat. Is it a 13 footer or an Arrowsport? (can't be both ) The Arrowsport is around 16' depending on age. The 13' boat was called an Arrowsprint.

If you have an Arrowsport then I agree with FrenchPhil; if it's an Arrowsprint there's a chance you'll plane off 4 up.

[Pat]

Originally Posted by TheOrs

My old 15 footer (unknown make) would plane off with 4 up (just) using a 50HP Merc & that was pre-ICOMIA. I think it had a 13" pitch prop.

Pat; I'm a bit confused about your boat. Is it a 13 footer or an Arrowsport? (can't be both ) The Arrowsport is around 16' depending on age. The 13' boat was called an Arrowsprint.

If you have an Arrowsport then I agree with FrenchPhil; if it's an Arrowsprint there's a chance you'll plane off 4 up.

My mistake, TheOrs - it's an Arrowsprint. Fletcher made so many Arrowwhatevers! Front bench seat, back seats are just a cushion either side of the centre channel leading to the sump, with a little triangular cushion on each side so you don't injure your delicate self.
What do you think my best bet at a prop would be? Or two different props for different loads? I'm not too bothered about speeding around 4-up, I'd just rather it didn't plough through the water like an old barge. Getting up on the plane would make a world of difference. The engine runs like a champ, starts first turn of the key but has never been tached - I've only had it in the lake a few times since I got it. The only "instrument panel" is the overheating light on the front of the engine itself! This is definitely a budget special... hence I don't want to pour loads of money into it. Hell, my tach coming from the states is £11 plus shipping, same idea as a TinyTach but cheaper.

Your thoughts are very welcome, can take pics of the engine setup if that's any help. Some people have told me "No, raise the engine way up!", others have told me to drop it down a couple of notches. I do know that when I bought it, the fella had a sandbag up in the bow. Got rid of that, weight that I can easily replicate with more fuel in Jerry cans if needed.
A bit confused as this is all new to me- for the last 17 years I've been either sailing light dinghies (gave up when I discovered girls and beer), or using a 12ft "With" fibreglass dinghy with a 4hp outboard to commute to the place I have on an island, from the mainland. Never really needed to worry about getting it up on the plane, it just plodded there. Now I'd like to go a bit quicker, and whereas the boat is great with one or two, with 4 in it it's about as fast as the With was!

Any and all prop suggestions are welcome... oh, and if anyone needs tech advice on old VW Golfs, just ask...

[Pat]

Oh, something else - once I fit my power t/t, will that be any help? As in, it might get it up on the plane trimmed right in, then I can trim it out a bit for speed? I'm pretty clueless about these sort of things, but suspect that most of you fellas started off with shitty boats and low powered outboards like mine, then learned from there?

[TheOrs]

Originally Posted by Pat

Anti-Cavitation plates are about even with the bottom of the hull.

This is correct for your boat. Don't bother moving it up; that's really only for high performance stuff.

Originally Posted by Pat

A pair of Doel fins are on it.

Have you tried taking them off? They are there to lift the stern & hence plane off quicker but they will increase drag once planing.

Originally Posted by Pat

Oh, something else - once I fit my power t/t, will that be any help? As in, it might get it up on the plane trimmed right in, then I can trim it out a bit for speed?

Probably'll help a bit.

To choose a prop you really need a tacho. Generally, the right prop will allow you to turn max rpm at WOT (wide open throttle) with your standard load. You need to know the max allowable rpm for your engine & try different props until you can hit that rpm but no more. I think 1" in pitch equates to about 200-250rpm. If you want to pull skiers, drop a couple of inches in pitch from the optimum.

As your boat is small the weight of an extra passenger will make a proportionally greater difference than it would to a larger, heavier boat. I have similar problems. 1 up it's lively, 3 up it's sluggish.

Try looking on eBay for some props to try; you can always sell them on when you've chosen the right one.

HTH

Darren

[Burty]

tony, sluggish isnt the word!!! wait till you try cye behind it! for a small bloke he creates a shit load of drag!!

[Pat]

Great stuff TheOrs, thanks - plenty of stuff there to think about! There are always a good few yam props on Ebay, so I can try a few different ones. Or there is an outboard breaker near me, he might let me take away a few and then bring back whichever ones don't suit. I'll try it without the fins as well - they do make it bloody awkward to get reeds untangled from the prop with the boat in the water, as well!

[Pat]

I can just imagine next time I go out to the island... ""ok everybody in the boat, let's see how this goes" - 2 minute blat - "ok everybody out, let's see how it goes with just me". Change prop, repeat and repeat again... maybe I need to buy a few bags of stones.