Prop size

[carbineone]

Ok I have a question.In my avitar you see I have a little 10 GW Invader mini speedboat.I just put a 1974 Evinrude 50HP on it and the engine came with a 13x19 pitch prop.The RPM range in my manual says 5000 to 6000 WOT.What your best guess how this prop will perform or should I just change it before I even attempt to take it out if it will be way off?..The boat of course is very small and light so from reading here if I understand correctly I may need the high pitch.Anyway take your best guess as what you think.I am going to install a Tach also before we take it out with the new motor this weekend...Just wanting a estimate what to expect...Thanks

 

[steelespike]

Re: Prop size

Run it with the 19 and get a well tested base line.
al or ss prop? max rpm and speed by gps if possible.

 

[carbineone]

Re: Prop size

We are actually going to take it out this eve for a test but have no tach or GPS right now.Will just have to see how it works by ear first.We had a old 1963 Johnson 28HP on it before and it ran probaly around 35MPH and thats a guess and the Rpms seemed good.Just wanting to know what to expect on a small light boat with that much pitch..Someone maybe should be able to make a educated guess on performance but will update this after the test.If it work good by ear we will just run it that way...Thanks

 

[carbineone]

Re: Prop size

Well me and the boy took the Invader out this eve and the Evinrude 50 ran perfect.I was skeptical as we bought it for 300.00 on craigslist and he said it

was a good motor and so far he was not lying.With the 13x19 pitch prop it ran very smooth and it will plane out in less than 3 seconds so that is very good I believe.I have not got the tach hooked up yet but Rpms sound very good by ear anyway.Not overeving for sure but maybe a slight bit low.Also have not had the GPS in there yet but I estimate with me at 220 lbs and the boy at 140 we were doing no less than 50MPH.It is a rocket. I may raise the motor around one inch more possibly but may not as it seems to fly the way it is now.I am sure with some fine tuning we could achieve 55MPH but probably not neccesary.Heres a pic of the 50 we mounted.....If you like boats and do not own one of these little Invaders you need to find one.The handling and stability of them is almost unbelievable.They are a blast....

 

[steelespike]

Re: Prop size

Thats a cute little boat.The 50hp prop selection here goes to 24" based on your little boat I would think properly setup you clould probably run a 21 or 22".
I doubt your reaching 50 at this point.50 is kind of a magic number not often seen on small stock relatively fast boats.When you approach 50 It begins to take a lot of hp to gain a little.Be sure the throttle opens all the way and motor is in excellent tune.
work on the height and prop selection.
Your actual figures will tell.Run the motor as high as possible.Some tolerate minor venting to get the most height.The more sofisticated props will allow maximum height with minumum venting.With that little potato chip; wear your pfd and be aware of the waters ahead.Doesn't take much to get in trouble at those speeds.
Early in the morning or quiet evenings are a good time to test.Sometimes a gently rippled surface will run faster than glass smooth.Would be interesting to see how it does with a 140 pounder alone driving.

 

[carbineone]

Re: Prop size

Thanks,we are going to borrow my brothers handheld GPS unit and maybe see what it does actual tomorrow.I know it goes fast.I have had several bigger boats in the past so can somewhat judge speed but only a GPS is going to tell for sure.We are going to mess with the trim and such too but the waters really cold here in Nebraska and I do not even want to get in and change that right now...I am sure with the kid in there alone it would go much faster but at this point he is not even of age to operate it alone but he will be in July but even then it will be towards summers end before I think he may be ready to solo so to speak..I am contemplating raising the motor a inch but have not decided.The motor itself runs very nice.I was happy knowing that as it was a used motor of course.I did not even run it before I brought it home but did turn it over and check for spark and the bottom end oil and if it went into gears...The guy seemed real ohnest and turns out he was..Goodluck for a change.I had a lying SOB sell me a Mercury and shipped it to me and it was not only in non running condition the motor was locked up solid and nothing like he told me on the phone.Did not pay alot for it but was still out about 100.00 but that is a alot of money for me.I was able to get the purchase price refunded by Ebay but lost the shipping.Cannot even talk about that I get so angry...

 

[steelespike]

Re: Prop size

Boy thats a shame.There are some real dirtbags out there.You should be able to part it out on ebay or craigslist.I did that with a Johnson that got damaged in shipping.