De-powering to 10-25 hp ob motor?

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mkrawats
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Joined: Mon Mar 17, 2014 12:16 am
Sailboat: MacGregor 26X

De-powering to 10-25 hp ob motor?

Post by mkrawats » Mon Aug 19, 2019 9:35 am

Anyone running a lower 10-25 hp ob motor? If yes, what is your experience?

My Evinrude E-tec just fried. EMM (onboard computer) destroyed. Spark plugs completely black. $2500 repair bill. My dealer suspects the cause may be due to excessive low rpm usage. We just don't run our boat at plane much.

Therefore, it may be more suitable for my next motor to have just enough power for full displacement mode + a little extra in reserve for super windy days and power through squalls.

Some of us owners may have installed 10 hp motors. But my mechanic is concerned that 10 hp may be insufficient. I just wish to learn from you your experience. Any recommendations or regrets?

bobflshmn
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Re: De-powering to 10-25 hp ob motor?

Post by bobflshmn » Tue Aug 20, 2019 11:37 am

I have been running a 25 hp. since I purchased my boat 3 years ago, PO installed. I can run for two days on 6 gallons of gas. Top speed is about 10 knots with ballast empty. I never empty the ballast and I can still run at 8 knots with about 3/4 throttle. I have an older 3 cylinder Suzuki which I would not recommend as it is a bit loud. Additionally the motor did not come with a power tilt so I added an after-market. I this motor ever fails on me I don't think I would increase to a larger motor as this does great for us, and fuel consumption is great compared to others I have talked to. Plus it is easier to get on and off with the smaller foot print.
Bob

MacAxel1
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Re: De-powering to 10-25 hp ob motor?

Post by MacAxel1 » Wed Aug 21, 2019 6:28 am

I've had a 50 hp Honda on my boat and switched to a 30 hp Yamaha when it was stolen.

Personally the 30 hp is ok, but with family the 50 hp was much better. We could get to distant anchorages much quicker, the ride was more entertaining for the kids and overall they enjoyed it much more.

The 30 hp runs at approx. 10 knots, but is then really working hard, so I do not like that. I'd rather go slower at 5-7 knots which is really nice with that motor as you hardly hear it, but the kids start to complain quickly because they get bored.

So, it depends.

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Seapup
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Re: De-powering to 10-25 hp ob motor?

Post by Seapup » Wed Aug 21, 2019 8:49 pm

Therefore, it may be more suitable for my next motor to have just enough power for full displacement mode + a little extra in reserve for super windy days and power through squalls.
I ran a honda 50 for a few years, then suzuki 90 for a few and then suzuki 20 on my :macx: . The 90 was fun for afternoon and daytrips, but we rarely ever went above displacement speed 99% of the time the way we used our boat. I liked the 20 just fine. It would not plane my heavy boat at all, but purr all day at 6mph under half throttle which was about 18mpg. I tried 4 different props and nothing could get it over the bow wave at 7mph so the extra hp from about half throttle up was wasted. I never ran my larger motors over about 6-7 mph in rough water and bad weather so it performed the same when chugging along. I think a 9.9 would have preformed identically. The main downside to it was less thrust when docking, but it was pretty easy too get used to and in some ways a little more predictable.

I bought the suzuki because at the time it was relatively cheap and 300cc fuel injected vs 200ccc carburated for the rest in that class. Tohatsu now has a similar fuel injected 333cc 9.9 with 12a alternator that looks pretty nice. I have had a few yamaha high thrust 9.9s and they are definitely my favorite for a displacement hull, but cost around 3k vs 2k.

beechkingd
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Re: De-powering to 10-25 hp ob motor?

Post by beechkingd » Fri Aug 23, 2019 12:03 pm

bobflshmn wrote:
Tue Aug 20, 2019 11:37 am
I have been running a 25 hp. since I purchased my boat 3 years ago, PO installed. I can run for two days on 6 gallons of gas. Top speed is about 10 knots with ballast empty. I never empty the ballast and I can still run at 8 knots with about 3/4 throttle. I have an older 3 cylinder Suzuki which I would not recommend as it is a bit loud. Additionally the motor did not come with a power tilt so I added an after-market. I this motor ever fails on me I don't think I would increase to a larger motor as this does great for us, and fuel consumption is great compared to others I have talked to. Plus it is easier to get on and off with the smaller foot print.
Bob
Which trim unit did you go with?

SolarSailor6
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Joined: Mon Jun 17, 2019 8:12 am
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Re: De-powering to 10-25 hp ob motor?

Post by SolarSailor6 » Sun Aug 25, 2019 1:12 pm

I run a 9.9 hp Yamaha 4 stroke long shaft high torque engine with "power prop". I can achieve hull "displacement speed" on my MacX of about 6.4 mph on 1/3 throttle. 10 mpg on average or 0.5 gallons per hour at that RPM Setting with water ballast full.

If you are not in a hurry, you can do 50 mile days with ease.

Ken
Lexington, KY

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opie
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Location: Wilmington NC, BF50A Honda, 1999 MacX, "Marin"

Re: De-powering to 10-25 hp ob motor?

Post by opie » Mon Aug 26, 2019 3:26 am

This topic is interesting since my 1999 Honda BF50A is getting old.
The admiral enjoys going about 6 kts. She says she gets to see more things....
One question: We have inlets with swift currents at peak times, maybe 4 kts.
What is max speed of 9.9 hp? Of 25 hp?
thanks.

bobflshmn
First Officer
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Re: De-powering to 10-25 hp ob motor?

Post by bobflshmn » Mon Aug 26, 2019 11:02 am

beechkingd wrote:
Fri Aug 23, 2019 12:03 pm
bobflshmn wrote:
Tue Aug 20, 2019 11:37 am
I have been running a 25 hp. since I purchased my boat 3 years ago, PO installed. I can run for two days on 6 gallons of gas. Top speed is about 10 knots with ballast empty. I never empty the ballast and I can still run at 8 knots with about 3/4 throttle. I have an older 3 cylinder Suzuki which I would not recommend as it is a bit loud. Additionally the motor did not come with a power tilt so I added an after-market. I this motor ever fails on me I don't think I would increase to a larger motor as this does great for us, and fuel consumption is great compared to others I have talked to. Plus it is easier to get on and off with the smaller foot print.
Bob
Which trim unit did you go with?
I went with the CMC PT35 from Cabels. Was on sale at the time I purchased it with free shipping. I have had it two years and it has worked great.

Alexis
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Re: De-powering to 10-25 hp ob motor?

Post by Alexis » Mon Aug 26, 2019 2:23 pm

Hi,

My 1996 Mac 26X came with an old 9.9 2-stroke Nissan. I sail my boat on a lake, which sometimes have pretty strong winds and short waves, but no swell of course.

I am quite happy with the OB. It pushes the boat at hull speed and has enough power for my needs. I like the extreme simplicity of the engine: its maintenance and winterization are almost non-existent, this means more time on the water!

Downsides are: it is very noisy, and it isn't very practical (no power tilt nor electric starter) but it is light enough and I don't mind having to open the helm seat.

If you don't need to go fast, a smaller engine offers a tremendous economy (these things are expensive!). 9.9 is on the lower side, if I had to change my engine I would get a 15 minimum and no more than 25. The 25 - 45hp range doesn't make sense IMHO because you need at least 50 to plane the hull and may be overpowered for hull speed.

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Tomfoolery
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Re: De-powering to 10-25 hp ob motor?

Post by Tomfoolery » Mon Aug 26, 2019 3:36 pm

Alexis wrote:
Mon Aug 26, 2019 2:23 pm
If you don't need to go fast, a smaller engine offers a tremendous economy (these things are expensive!). 9.9 is on the lower side, if I had to change my engine I would get a 15 minimum and no more than 25. The 25 - 45hp range doesn't make sense IMHO because you need at least 50 to plane the hull and may be overpowered for hull speed.
The 9.9 on my Aquarius was adequate for reasonably calm conditions, but not enough when pounding through waves and wind. It was a displacement hull, but that didn't matter as waves would stop it in its tracks. More thrust would have been nice to get going again after hitting the wall (wave) repeatedly. Very hard to make progress.

I also agree that much more than 15 hp would be a waste, as you need a lot of thrust to get the bow up high enough to semi-plane. A 25 would likely, IMO at least, just put the bow high and burn more gas but barely go any faster. That transitional speed where steering is lousy and you're just plowing a big wake while draining the gas tank at a goodly clip. :|

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mallardjusted
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Re: De-powering to 10-25 hp ob motor?

Post by mallardjusted » Sat Aug 31, 2019 1:00 pm

I can do hull speed extremely economically with my Yamaha 70 (and it only weighs about 10 lbs more than a 50). But I can also do 23mpg if I want to. My kicker is a 9.9hp Mercury, and can push the boat at or near hull speed. But with some currents and winds, I don't think I personally would go below a 15 for a main engine.

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dlandersson
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Re: De-powering to 10-25 hp ob motor?

Post by dlandersson » Sun Sep 01, 2019 5:40 am

Ditto. 8)
mallardjusted wrote:
Sat Aug 31, 2019 1:00 pm
I can do hull speed extremely economically with my Yamaha 70 (and it only weighs about 10 lbs more than a 50). But I can also do 23mpg if I want to. My kicker is a 9.9hp Mercury, and can push the boat at or near hull speed. But with some currents and winds, I don't think I personally would go below a 15 for a main engine.

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