Mercury High Five question

[1973Chieftain]

My boat is a 24' aluminum Starcraft cruiser, weights about 4500 lbs loaded with people. Currently I have a 3 blade aluminum 17p on it running at about 4150 rpms... max is 4200 for my Mercruiser 898 190hp. I hit 38mph with this setup. I wish to improve handling, particularly for watersports. I'm considering either a 4 blade aluminum or a 17p High Five as I have read a lot of positive reviews of the High Five but my main question is can i switch from a 17p 3 blade AL prop to a 17p 5 blade stainless without loosing much rpms? It seems logical that rpms would go down but I have read in forums that folks stay with the same pitch. Has anyone tried it? Thanks!

 

[alldodge]

My boat is a 24' aluminum Starcraft cruiser, weights about 4500 lbs loaded with people. Currently I have a 3 blade aluminum 17p on it running at about 4150 rpms... max is 4200 for my Mercruiser 898 190hp. I hit 38mph with this setup. I wish to improve handling, particularly for watersports. I'm considering either a 4 blade aluminum or a 17p High Five as I have read a lot of positive reviews of the High Five but my main question is can i switch from a 17p 3 blade AL prop to a 17p 5 blade stainless without loosing much rpms? It seems logical that rpms would go down but I have read in forums that folks stay with the same pitch. Has anyone tried it? Thanks!

IMO more blades more drag and more lift. The high 5 will give you more lift but will not give you anything else except more trouble. If you want to pull water toys under heavier loads go to a 15 pitch with more diameter (if possible), or get a 15 pitch and have it cupped. Down side of lower pitch, higher revs when not pulling loads so watch over rev.

 

[steelespike]

The calculator says you can't make 38 with those numbers.I'm using 1.84 gear ratio Your indicated rpm and speed.
Right now the only number we know for sure is the pitch.If the speed is by gps it should be accurate.
Do you know the gear ratio? We shouldn't make any prop changes until we know your numbers for sure.
My suggestion if we proof the numbers would be a 4 blade 16". Your motor is rpm challenged Should maintain
close to present rpm but give you better hole shot,stay on plane easier at reduced throttle and may handle better around the dock.
Forgot to mention a high 5 is probably a poor choice for your motor.

 

[1973Chieftain]

Tha KS for the advice Dodge and Steelespike! Steel, the speed was by GPS and the rpms was by the tach on the dash. The engine and drive were installed by a shop, but the drive had come off a 260 hp mercruiser of mid 80 ' s make. Wish i had that bigger engine, but oh well. I'm not sure how to determine the gear ratio, is it stamped someplace on the drive?

Would it matter much between aluminum and SS in this application do you think? I have read extensively on the pros and cons of SS but it seemed most benefit happened with high hp engine which I doubt could be applied to mine

 

[steelespike]

My info indicates the ratio on a 260 is 1.5 that makes the numbers work better. 4150,1.5 ratio,17" prop 38 mph 11% slip.
I would think that holeshot is pretty slow. The 4 blade 16" pitch I suggested should help.Without having to watch the rpm as close.
as going to a 15" would. It may cost a little top end.