Yet another prop question

[Dave Abrahamson]

I'm running a 12 3/4 x 17 stainless on a 1983 Johnson v4 90 HP (J90TLCTE). The motor is mounted on a 1975 Wellcraft Airslot 165. I'm turning about 5300-5500 RPM WOT. top speed is about 35 MPH (cheap water pitot speedo). It seems like a smallish prop for a 90HP but the r's are where they are supposed be..right?<br />Is it just because it's a heavy old boat? I see other people posting that they run a bigger and higher pitch prop on 90's, some on bigger boats even. Is my motor a dog? Or is my old boat a barge?<br /><br />Thanks in advance<br /><br />Dave

 

[Dhadley]

Re: Yet another prop question

Ah, the Air Slot. Wow does that bring back memories.<br /><br />Anyway, thats a pretty small diameter. The pitch doesnt sound too far off but we need to get the rpm's up on that deal. I'd like to try raising the motor but with that small of a diameter I'm not sure we can go very far. <br /><br />If I were doing it I would go up some just to see how many rpms we could gain. It may vent in the turns or on takeoff but all were after is the rpm effect right now.<br /><br />Those ol 'Slots werent very fast but they ride good.

 

[DJ]

Re: Yet another prop question

I always thought the 90's spun a 13 1/4" wheel?<br /><br />The RPM's are borderline low, but should be OK. You DEFINETELY do NOT want more pitch. More pitch will lug the engine and eventually destroy it.

 

[rickdb1boat]

Re: Yet another prop question

Must be a pretty heavy boat, as the prop selector calls for either a 21" or 19" prop. They do have a 13-1/4 X 17, which sounds right if your boat is heavy and your motor is running to full potential. Could be that the boat is waterlogged and you are pulling more weight than you think. Run it through a truck scale and see what it weighs... Is the cavitation plate on the lower unit even with the bottom of the hull?

 

[Dave Abrahamson]

Re: Yet another prop question

WOW! You guy are quick!<br />I didn't mention that I'm running a Doel-fin, but the RPM's really didn't change after installation.<br />I'll try and raise the motor up a hole and see what happens Dale. And yes, she does ride nice <br />Rick, I have a scrapyard here that I do business with and they will let me weigh the beast. The NADA says 1100#....we'll see. It just may be watterlogged after all these years and put on a few extra lbs....? <br /><br />Thanks Guys, I love this site!!<br /><br />Dave<br /><br />P.S I really don't need extra speed, I just want to make sure I'm not lugging/hurting my Johnson

 

[Dhadley]

Re: Yet another prop question

Ditto on the PS. Thats what we're concerned about too.

 

[BillP]

Re: Yet another prop question

Those airslots are definitely heavy and that's why the prop "is". 35 mph with a 90 is respectable for that rig.