Propellor selection

[Destination Sea]

Hi maybe some can help. I tested the boat today and managed to obtain about 4200-4300 rpm. (engine rpm 4500/5500) with the standatd propellor if not mistaken 17". The spead was tremedous for me and personally i dont need it. But iin order not to damage the motor i wish at least to have rpm range of 5000. The boat had 3 people on board an about 75 l petrol. what propellor size appx would one suggest.
thanks

[Granitu]

http://www.rbbi.com/folders/prop/propcalc.htm


http://www.csgnetwork.com/marinepropcalc.html


calculate it here and test.. that's how i am obtaining better results with my boat. important is to observe that the boat does not shake (hafna vibration)

that means that the propellor is stressing the outboard which is no good to the engine. this info was obtained from a very expert outboard mechanic

search a little about the pitch and suit it to your needs

hope it helps

[skip]

Sounds like you're definately over propped. Was acceleration quite sluggish.......?

Based on research the optimal WOT range of the ETEC 90 is 5000-5200 and this is what you should be aiming for with a typical load.

Ie. Determine what load you would run the most (are you the type who likes to go out with full fuel, water etc), do you normally tend to go out with 2-3 people etc.

The standard prop for most 90hp is a 15P.......if you stick with the same prop make/model for comparison then for every inch of pitch you reduce you will gain 200rpm. But that still only puts you at 4700rpm

Drop from 17 to 15 and your RPMs will go up by around 400rpm.....

You're basically in the same situation as me in that you've set your boat up heavy, alot of fuel for fishing, probably a water tank, then the auxillary etc........

On mine the std 15P 3 blader that came with the engine only gives me 5200rpm full throttle trimmed (by the way did you trim the engine all the way up so that it slips at full throttle and then down a bit?) and then measure your RPM?

From there I tried a Solas 4 blader (for improved stern lift and mid range/acceleration) as my holeshot was terrible, it's a D4x13.25x13P and with this I can sit at around 5650rpm with 3 ppl, full fuel, water configuration for fishing, whilst on my own if I get some air I will hit the limiter as I get 5950rpm going above 6000 with air.........WOT for my engine is 5250-5850 so I came to the conclusion that my ideal pitch is 14 which I am getting done for me as A 14 pitch prop isn't really made, you've got 13 and 15 so I had no choice but to get one arranged by a prop specialist in the UK.

Confirm that your current prop is def a 17. If it is then you need to drop to a 13P.....I know it sounds low but you're running a heavy load..........you need to gain 800rpm so that your engine sits in the optimum WOT range and isn't being over-stressed......

4200-4300 +800 will put you at 5000-5100 which is as close as you're going to get and probably just right because like that if you go out with less people or fuel you're unlikely to go over 5500 and if you go out with more people you won't drop below 4500rpm .......what's important is that you stick with a largish diameter prop, the Solas Amita 3 in 13P is 13.75 inches x 13.......

If you want I have a Solas Alcup 4 blader, D4x13.25x13P which is coming off my boat this weekend which you are more than welcome to try and evaluate.....but you will need to go to Ronnies marine to get the bush kit which should be around ?25 (Evinrude run 13 splines)

Speak with RLR and see if you can try out one of the 13 pitch 3 blade props, not sure what arrangement you had with them about the prop and whether or not you can change.

This weekend I will be trying a Solas Amita D3x13.75x13P on my boat to see how that goes whilst I'm waiting for my 14P 4 blader to come down from the UK which I'm hoping will be my ideal prop. This is why I've put my existing props (the one that came with the engine 15P and the 13P 4 blader up for sale) so that I end up with two props (one main, one spare) that are ideal.

Unfortunately it's alot of trial and error and there are no prop shops in Malta that carry a range for you to try, though some engine sellers do....

[Destination Sea]

thanks skip very informative. I will try out the options at rlr. had spoken to joe and he said try it out first.. it think the 13 would be good by it think its a matter of trial as you perfectly stated and exprienced. Thanks  granitu i will do the test.
skip i will have to check it out again cause i only tilted up to half of it.