prop help PLEASE

[my1stboat1]

1988 85hp Force outboard 856x8a

the factory Prop is an ALUMINUM 13X17 ... the engine with this prop 1 person on the boat thats ME 220 Lbs and the engine at WOT is turning 4500 Rpm which is at the Low end of the RPM limits... the engine bracket states 4500 to 5500 .... THe Boat goes about 32mph ...

I bought A used STAINLESS prop MICHIGAN 13 1/4 X 17 is stamped on it.. But the guy I bought it from said he had it repitched to a 15 pitch and theres a 5 stamped over the 7 on the hub of the prop and a 15 stamped on the blade of the prop...

Installed prop on boat... Just me on boat and at WOT the boat Lost RPM it not Operates at 4200 RPM wot and 30 MPH...

I want the Rpms Higher Like 4800 To 5000 Rpm.... WHAT DO I NEED TO DO TO SEE THESE RPM NUMBERS...


thanks

 

[krovar]

Re: prop help PLEASE

is it the prop that has long slotted ports with wide blades, if it is they are made to grab lots of water, tryed the same thing, and the same thing happened to me

 

[my1stboat1]

Re: prop help PLEASE

yeah it is Krover... It has large cupped blades and Long spline slots in it...Ill tell you what though I was happy with how smooth the engine operates with the heavier prop on the unit, But the loss of rpm was shocking .. What did you do with your setup

 

[krovar]

Re: prop help PLEASE

tryed raising motor and got the rpm up but would get slip or cavation when the boat first plained out, dropped engine back down and found a 13.5x18 raker, 5800 rpm trimmed 48 to 50 mph, the trick is to find a good used one to rebuild because there around 650 dollars new. im running a 115 johnson you will need a lower pitch

 

[SparkieBoat]

Re: prop help PLEASE

lifting the motor as high as you can with out cavitation...may even consider a manual jack plate..you want your rpms more in the mid 5k..i have heard that you can only repitch a prop 1 pitch not 2. so I am not sure what you have there. but you should borrow a 13 pitch prop and see what happens..looks like that would put you over 5k rpms

 

[steelespike]

Re: prop help PLEASE

What boat are you running. length,dry weight?Brand,model glass/aluminum?
The 17 seems like a reasonable size with a 2.00 ratio.
Raising the motor if needed is a good idea and could gain some mph and rpm.
Is it a through hub exhaust or non through hub.Through hub is available in 10,13,15,17,19,21. here at iboats. I think you can see a 13 is far down the list used for somrethiung hard to push like a pontoon or large heavy boat. You can see a 17 would appear on a boat that an 85 would be expected to be on. The non through hub are limited here; 15,17,19.
To make a long story short I think you have a motor or setup issue unless you you have a really heavy boat. imo, a 15 or 17 should produce over 5,000 rpm and speeds 35 to 40 +mph.

 

[my1stboat1]

Re: prop help PLEASE

the boats an 1988 bayliner, Center console..... Not sure off hand what the dryweight it... but the engine runs flawlessly... Comps good, ignition is good, has no plugs, fuel pump, regulator, waterpump and this stainless prop.... THe engine has always ran great... The timing is set statically at 28 degrees.... as far as engine height the prop when in the lowest position is dead even with the keel on the Hull... I do trim it up when out on plane and the rpms obviously increase but maybe 100 200 rpms

 

[SparkieBoat]

Re: prop help PLEASE

I will assume your motor is in the top holes..you could most likely move it up to the 3rd or 4th hole..it may want to cavitate a little on a hard turn..maybe not. but you need to get your motor WOT RPM to over 5K