My friend with an issue.

S

steplift20

God
My friend ( yeah I have one) has a 19 foot bay liner with a 2018. 150. 4 stroke mercury. He says his top speed is only about 25 to under 30 mph. He doesn’t know the prop size . He is new to boating and he also says it cavitates some times. I know what I told him but I would l8ke to know what you guys think? I don’t know to much about 4 strokes since I still have my 2 stroke 150 mercury he also said his rpm’s tops out about 4000 rpm’s. Thanks for any reply’s
 
4k rpms is around cruise speed on 4 stroke. Wrong prop as you suggested, or, if it had been running faster, it could be a number of things including dirty bottom of hull, or possibly the shift linkage needs proper adjustment? Basically need more info - did it just start doing this behavior, OR has it never run more than 25 - 30? He should be turning well over 5000 rpm, on up closer to 6k in my opinion.
 
Hi Blue. He just got the boat and doesn’t know to much about boating or the engine. I told him to see what prop size he is turning. I told him on my 150 2 stroke I’m turning a 15 x 17 inch prop and it’s a perfect marriage. Bu5 I don’t know if 4 strokes are the same. But is sounds like something is not right
 
Hi spare. Yes it has bottom paint and I ask him it could be covered with barnacles but he told,e it’s clean. I told him to check the prop size. I hav3 a question ? A 2 stroke or a 4 stroke Same hp would it be the same speed? At W.O.T. ? I don’t know ?
 
gear ratios varym quick google search says 2/1 or 2.4 to 1. Your old school 150 would have been 1.87 or 2.00. Its goinf to take a little higher pitch than your old engine. merc has a prop speed calculator online to figure it out
 
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