9.9 or 15 HP Outboard on 25' Boat?

[foolproof]

No real current in Lake Michigan, is there?

But seriously...hull speed is hull speed, regardless of which way the boat is going. Assume for a moment you are anchored in a 4 knot river...what would the knot log read? If you said 4 knots, you are correct. Of course, being anchored, you won't make any headway against the current. However, if you haul the anchor in and throttle up against the current at hull speed, your knot log will read 6 or 7 knots, but you're only making 2-3 knots against the shore. Of course, if you headed down river you'd be doing 10-11 knots against the shore, but again, your knot log will only read 6-7 knots. The boat doesn't know (or care) which way the water is flowing!

 

[RECESS]

Sorry but if the engine you have will push the boat to hull speed (non planing, displacement hull), more horsepower won't make you go faster, current or no. You're gonna make hull speed against the current, but won't make anything more over the bottom.

example- hull speed 6 knots, 5 knot current- you're gonna go 1 knot. No matter WHAT horsepower you're running.

My experience is quite different than what your calculations are saying. Our O'Day 25 was heavier than many other 25s. We had to enter the Carabelle river. Often at the mouth of the river it got a little shallow and the waves would stack up. With an 8hp you often would get slowed down significantly going against both the current of the river and an outgoing tide. With a 9.9hp we would motor right through. It was not a fun experience to get tossed about with waves stacking up as you entered the river. An 8hp would get you to hull speed in light conditions but it would not keep you there in heavy conditions. We also go 30 to 50 miles off shore. You can leave in 1-2 ft and when you are offshore a line of thunderstorms can make it 8-10 ft very fast. The extra torque on the 9.9 mad a difference in keeping the boat from being tossed around.

I could reach hull speed on a clam day with a 9.9 on my Pearson 323, but I doubt I would want to step down from my 23hp Volvo when it got snotty.

 

[MrBill_FLL]

Well we pulled the trigger for the Tohatsu 15hp 20". We had an old Johnson 15 HP 20" and it seemed to work ok, so we went with the 15hp after much debate. One nice thing is the charging system is bigger on the 15hp. Thank you all for the good information.
Now, due to the weight difference we need a new mount. Who do you recommend? I have been looking at the Garelick ones and have come across a few that are on deal, but they are the 9.5" drop down. The boat is 65 miles away for the winter and as soon as I get back up there I am going to do some measuring. In the meantime, any thoughts on the mount?

Thanks!

20" shaft..... :naughty:

You have not (yet) experienced the engine coming out of the water as you try to make way against a short choppy sea. hopefully that won't happen to you in a narrow channel. (like me)


Good decisions come from Experience. Experience comes from making bad decisions.

I suggest you reconsider...

 

[ChiTownSail]

20" shaft..... :naughty:

You have not (yet) experienced the engine coming out of the water as you try to make way against a short choppy sea. hopefully that won't happen to you in a narrow channel. (like me)

Good decisions come from Experience. Experience comes from making bad decisions.

I suggest you reconsider...

Thanks for your input. I have experienced that before, thank you. Although not an expert like yourself, I sailed Lake Michigan all last season and didn't have very much trouble at all.

 

[MrBill_FLL]

best of luck!



yep, got my T-shirt too...

 

[twistedline]

No real current in Lake Michigan, is there?

But seriously...hull speed is hull speed, regardless of which way the boat is going. Assume for a moment you are anchored in a 4 knot river...what would the knot log read? If you said 4 knots, you are correct. Of course, being anchored, you won't make any headway against the current. However, if you haul the anchor in and throttle up against the current at hull speed, your knot log will read 6 or 7 knots, but you're only making 2-3 knots against the shore. Of course, if you headed down river you'd be doing 10-11 knots against the shore, but again, your knot log will only read 6-7 knots. The boat doesn't know (or care) which way the water is flowing!

Interestingly if your anchored/moored in 15knots of current the knot log will read 15 even if your hull speed it 6.

Those Johnson 9.9/15's are great engines.