Propping Advise

[alldodge]

I would suggest start with the 14 3/4 diameter 21 pitch

 

[Scott06]

Find a local prop shop who will let you try a proper or two before buying it. With that small engine I don't think you have the power to get the revs up with a 21" prop. Would try a 19" 3 blade or 18" 4 blade. Did the same with my 17 ft sea Ray with a 135 hp 3.0. Same 2.0:1 drive. With a 19" was at 4600 rpm or so, a tad less when I tried the 4 blade vortex 18" pitch- aluminum and relatively cheap.

 

[steelespike]

Test with the Salas 21"
I wonder if the 13 3/4 X 21 is the right diameter for your I/O.
That may be why your test was odd.

 

[pyro225]

Diameter is too big apparently should be around 14 mark 14 1/4 I think that's why I've been buying all these merc ss prop

 

[alldodge]

Have any results yet with trimming?

 

[pyro225]

Not yet sorry being the uk its been raining for the last couple of weeks - hoping to get out tomorrow but its not looking too promising!

 

[pyro225]

on this though i have spoken to the dealer and they confirmed it would be 14 1/4 ally 21 it would come with so would the solar be too hard work to turn and maybe i should go with the 21 vengeance and that 13 3/4 (although that may be too easy!)

 

[pyro225]

hi guys - finally got ok bit of weather this morning. on a river very calm no flow either way today with the vengeance (paranoid about the solar as its too big and my engine doesn't react well to over propping if you look at previous threads) anyway on the plan flat out 28... i then lifted the gear at the back and we got a little faster but didn't get to the point you mention of bouncing up and down to which you lower... i didn't get any bouncing and got to 32mph however i kept going up and then the revs went higher and speed drops as obviously the prop was on its way out... so to sum up i found an extra 4mph... what do you think to this? I'm tempted as annoying as it is to get a 14 1/4 ally 21p prop as it came with from new and try again :/

 

[pyro225]

Bump...

Also relating to this I think - I went out for a trip on Saturday - had the Bimini up as it was spitting with rain and everyone want some partial cover except one person so I had 5 guys in the back and one in the bow. This is maximum weigh I appreciate but when I when full throttle with the leg all the way down it would not get on the plane and seemed to go about 15mph tops - would you expect that with the extra load? My 2 stroke 90 outboard would lose a bit (maybe 40 mph to 32-33mph) but not halve it ?

 

[alldodge]

Something about the numbers are wrong but the short answer from my reading is the motor is the basic issue. It's a 1.7L that produces 120hp and the torque comes in around 3800 to 4200 rpm. These motors for the most part are kept a WOT just to move the boat and the longevity isn't that great because of it. They are a great motor for trolling.

The reason your having trouble getting up on plane with a heavy load is because the torque comes in at such a high rpm. You need torque to pick the boat up, and even the gas 3.0 puts out more then this one. If you look at all the speed boats the gas always out performs the diesel, but in most cases the diesel will outlast the gas.

If you want to get up easier with a heavy load you need to reduce pitch, but then this will cause you to run higher rpms and more chances to over tach

 

[pyro225]

Thanks all dodge - here may be another possible problem - it has never been antifouled and has been in the river for a year now - and has a good coating of weeds/algae would that cause any of these issues - I've just spent a fortune on antifoul and will pressure washi it down and paint it ...

 

[alldodge]

will pressure washi it down and paint it ...

Part sounds good but not all, this would be a new area. Pressure wash will get rid of most the growth, but it should not just be painted. It needs to be sanded to rough it up, use acetone to clean, then some coats of barrier coat prior to the coating of antifoul

 

[pyro225]

Would this be slowing it down?

 

[alldodge]

Would this be slowing it down?

Sure it will slow it down

Here is my thought, painting a boat every so many years will cost a few thousand dollars. Putting the same boat on a lift will cost twice the cost. So after the second bottom coating, you pretty much paid for the lift