Hi Brett, i have a 1990 21 scarab 7.4 w/nose cone. i'm using a quicksilver 23p which seems to be the best for top end and also the boat rides nice and flat. i'm hitting 62-63mph 5000rpm. If this was your boat do you think a nice cup on this prop would be worth it? and roughly how much to do it? thanks in advance! Jeff

Hello,

Normally I like specific cupping added to QS Mirage propellers on hulls like yours. However, you are running quite nice at 13.91% slip and a good R level.
Next, I do think, thin the blades to a thin thickness curve cause you can with this HP to Wt. ratio you have and then induce the proper cup in the proper location to aid the bow with less button and we have a recipe for 1.25-3 mph.
It is $376 to do this and it will take about 2 weeks or a little less.
Call me and I can explain the details or just send in the prop and we can talk then.

Brett

(bobo1 - I hope you don't mind me hijacking your thread - I had a similar question for Brett)

Brett,

I have:
1985 242LS, twin 350s
58.4 GPS @ 5100 RPM
Mercury Quicksilver Lightspeed (replaced Laser II) props, Part #: QS5072X.
Dia: 13 7/8
Pitch: 21
Blades: 3

I'm looking for more top end. Should I go with a bigger prop and drop RPM to around 4600-4700? Should I have you lab my existing props or do you recommend a prop you can sell me?

Thanks.

Actually your propellers didn't replace the Laser 2's but rather are the Quicksilver branded props which allow for other marketing aspects for Mercury. Unfortunately it also allows less QC. Therefore the specs. are uncertain without measureing them.
That being said, I think dailing in the 15.69% slip you have and maintaining the R's could give you aprox. 2 mph.
We would ned to measure the props first.
And.............yes, EVERYBODY'S stock propellers vary.

Brett

Tired good night....................

Thanks Brett. I'll be sending my props in to you. G'night.

Thank you a ton Brett, i will call you when i'm ready to ship my prop! Thanks, Jeff

Hi Brett -

I missed my window to send you my props as the summer is here and I don't have a spare set. Do you have 2 RHR props I could buy and achieve the gain you calculated? Would Mirage Plus 13702s do it?

Thanks!


Thanks.

Labbing Mirage+ 21's at 14.5" with a little extra tip cup should work great for you. This will decrease the slip some and keep the rpm at the needed level.

Th props sell for $525 and the Lab work is $376.
Let me know if you have any other questions.

Brett