I don't think I need a 9.9hp for a Mac25

[MrBill_FLL]

fyi
http://www.boattest.com/resources/view_news.aspx?NewsID=3643

I really doubt anyone of us has enough hours on their prop for this to show up.


way back when I could waterski, I would run a 19" for skiing, and 23" double cup for speed... made all the difference in pulling people up.

 

[Doc_holiday]

I'm going to keep that ski story as my defense. If you ever saw the movie "grown ups" where the boat attempts to pull Kevin James up on the ski and the boat blows up- that was me and ever time we watch the movie, everyone breaks out in hysterics. One year in St Lucia while staying at a resort, they offered water skiing. It had been a while and a few pounds ago that I had skied. Anyway our friends each took their turns and I was not about to be outdone. My problem was never the slalom, but rather kicking off the second ski. I opted to have them pull me up on one. The boat revved and I bet I hadn't moved 20 feet plowing to get up when the motor blew on the boat. Everyone looked at the fat guy when skiing was done for the day. I'll go with they had the wrong prop.

Sorry, I digress. I like the 9.9.

 

[vizwhiz]

Something else to keep in mind when looking is to think about how far you can swing the motor side-to-side. I'm not sure it is any issue with the 25 since the motor mounts off the transom (no motor well), but the powerhead of the 9.9 is larger than the 6 by a significant amount. On the 26S/D the motor sits in a well and hits when swinging side-to-side. Just a thought about what might be in the way or what you can reach (controls, etc) with the motor mounted back there...

I'm currently working on an elevated steering control like Sum bolted on his to raise the tiller over the motor well.

 

[patrickfarley]

I would prefer the 9.9hp if I only wanted power. However, I am going to a 4stroke engine and don't want to deal with the extra weight that won't change much in the overall performance I need. My current 9.9 hp outboard puts out more power than I need so long as the waves are small. I think a smaller outboard with a longer shaft will make me happy.

I started out in sailboats that had no engine at all. I think that I will do just fine with a smaller outboard. I will just have to remember how much power I have and plan ahead.

As soon as I fix the transmission on my Suburban I will report back on the results of a 6hp on a Macgregor 25.

 

[mcfast]

Mac 25 has 6.43 knots Classic Hull Speed.
5 hp 4 blade prop
Knots
Gerr's Maximum Speed Under Motor
6.7 knots.
Optimum Prop Diameter 8.2
Inches.
New RPM 2369

 

[Piotr]

Mac 25 has 6.43 knots Classic Hull Speed.
5 hp 4 blade prop
Knots
Gerr's Maximum Speed Under Motor
6.7 knots.
Optimum Prop Diameter 8.2
Inches.
New RPM 2369

Sorry, I don't get it.

 

[walt]

The reference to Gerr's maximum speed under motor was interesting.

I found a calculator (not that easy to use) that said it takes 4.7 hp to get a boat similar to a Mac 25 or 26 up to the theoretical max hull speed - close to the 5 hp mcfast listed. Given that an electric trolling motor is enough to go against some fairly high winds, Ill assume that you need about 1 hp to account for wind.

So 6 hp should be enough to get to max hull speed for these boats in just about any condition - but you need all the hp available (by picking the right prop). Current.. hull speed is hull speed current or no current.

But going to higher hp is certainly nice with the tradeoff of weight at a bad spot on the boat. But now with the excess hp, you don’t need to worry about elevation (which I do - using the boat between 8600 feet and 450 ft makes a significant difference) and you also don’t need to worry about the prop so much.

You probably can counter the weight of the larger outboard in the rear by weight up front to some extent (my two golf cart batteries are as far forward and low as possible) but weight also in general slows a boat down - if that matters at all and it doesnt to most people as difference between a 6 and 10 hp probably is minor..

 

[patrickfarley]

I just bought a new to me 7.5HP 4 cycle long shaft outboard with a charger. I got it running tonight. The impeller looked new and soft. After cleaning the carb it starts and runs nicely. It has a bigger prop than my 9.9hp. When I put it in gear in the barrel it moves a lot more water at a very low idle.
Hopefully I will splash the boat soon and find out what kind of performance I will get.

 

[Tsatzsue]

More is better even if you need to use it only once in a while. 9.9 Johnson Sailmaster longshaft with a three blade sea prop. is what I have. Surprisingly it reaches hull speed but only above 3/4 throttle. Lots of grunt in reverse and forward. I find that that is important in docking and tight maneuvers. I wouldn't go with anything less.

Here is the only partial pic of the motor I could find. Tsatz at Hoppey's Landing in Fairhaven. Dingy on the foredeck for getting through Woods Hole....just in case it was rough.

 

[patrickfarley]

I just used my new to me 7.5hp Honda 4 stroke outboard. I am replacing a 9.9hp 2 stroke Johnson/Evinrude. I am in love with the Honda. Plenty of power. Drives right through the wind with no problem using partial throttle. I think the prop is a better fit for my boat and the new motor has a long shaft. With both of these improvements I need no more power.
Also this really has a reverse. The 9.9hp would slow me slowly, had to be the prop size. The 9.9 would drive it forward with great force but reverse did not work well.
I can tell the 7.5hp Honda does not have as much power but, I think the power it puts out is more useful with the prop and the long shaft. The 9.9hp had more power than I could use even in a pass going against the tide and wind.
Wind has been my greatest enemy when under power. I think the bow of the Mac 25 should be listed as sail area. When I was pulling into my slip today, with a good cross wind(9-14 mph) the engine seemed to give me a better grip to the water. Throttled down and still had good control and hit reverse which stopped me before I hit the dock.

Best of all the outboard was quiet as it sipped gas. Can't wait to try it out going to Cayo Costa.

Have to fix the transmission on my Suburban before I can go. I am learning to rebuild it myself.