countryboy26047
Petty Officer 1st Class
- Joined
- May 25, 2012
- Messages
- 303
Well, I'm sure ya'll are getting tired of my questions here, but I've got another and hopefully it's in the right topic... For those that don't know from my previous posts/questions, I've got a 16' SeaStar fiberglass tri-hull with a '75 merc 850 I-4 mated to her... After finally getting my tach fixed and feeling comfortable taking it up to WOT (since I now know I'm not blowing past the recommended 5,500 rpms), I have found that at WOT, I'm hitting exactly 5k rpm's, but can only get 31mph out of her, that's with me and the wife and minimal gear (maybe 450lbs total weight in boat), the boat supposedly weighs in at 964lbs dry weight w/o motor.. unfortunately I don't know the pitch of my prop, but seeing as the rpm's are almost dead in the middle of the "sweet-spot" I don't know that I should try to change the pitch.. my question mainly is, does 31 sound slow for this thing?? Also, I have manual T&T, so trimming it out once on plane is outta the question.. I have tried running it with the trim pin in the three holes closest the transom but only noticed a 1-2mph diff.
In the 3rd hole from transom, it planes out great at around 2500 rpm's and has perfect plane after 3500rpm's. I thought about raising the pin another hole, but worried I might get too much positive trim and cause cavitation... Any input is greatly appreciated.
In the 3rd hole from transom, it planes out great at around 2500 rpm's and has perfect plane after 3500rpm's. I thought about raising the pin another hole, but worried I might get too much positive trim and cause cavitation... Any input is greatly appreciated.
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