Trying to choose my new boat

[benri]

it's a 3 blade aluminium - if I'm not mistaken 19 pitch. Yesterday at one time it worried me a bit cause on two occasions it sort of slipped and left a hole in the water before accelerating... After that I began to think on whether pitching, etc. is right as I don't really understand in this area.

[skip]

What you're describing is prop slip, usually caused by cavitation, although it can sometimes be caused by a loose hub when the prop isn't tightened down enough.

A prop shouldn't cavitate under normal operation, especially if you are acclerating up on to the plane, but it can occur at speed when you have the engine trimmed up for optimum performance and you come off the top of a wave, causing the prop to slip as it comes out the water, or during tight turns.

If they have mounted your engine quite high, which alot of installers like to do as it gives higher speeds etc then it could be that your prop is running quite close to the surface and therefore is more prone to break the surface as your traverse over a swell. The solution to that is to switch to a four bladed prop which is happier running close to the surface, but before doing that you need to be sure what's going on and why.

You do lose some top end speed with a 4 blader, but get a better holeshot (accleration) and usually a more efficient mid-range cruise.

[rob1974]

I am so interestd in the minimum speeds bacause of live bait trolling.  Since I hope to have a boat in the next few months I'd like to know whether it is possible to troll close to 1knot with the main engine, or would one need and auxiliary for such use.

My fishing mate can troll with the main motor (he has a tohatsu DI) at low speeds, minimum 1.2knots, but he has to use bucket tied to the back of the boat.  Also, he can acheive such low speeds because the boats is underpowered, acheiving a max speed of 23 knots.

Rob

[Shaftbomb]

Trolling at one kts with a "big" motor you are not going to do him any good......for a 1-2 kts speed you will be better off with a small auxiliary.

[rob1974]

I think that this appies mostly to large (100hp+) 2 stroke motors.  I am quite sure that the 4 stroke motors can take slow trolling for extended periods without any particular problems.


I stand to be corrected.

Rob

[skip]

I think even big 4 strokes should be fine, I never had issues with a Mercruiser 5.7L TBI V8, I just used to keep an eye on the plugs over winter which maybe fouled a tad more than normal use.

Std carb two strokes definately don't like it at all, and well even my Tohatsu 90 Direct Injection doesn't seem too happy, see my update on the post 2 strokes vs 4 strokes for trolling.

[rob1974]

My fishing mate has a 50hp Tohatsu DI and it never gave any problems while trolling at the slowest of speeds. 

Rob