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Go Back   SailNet Community > On Board > Gear & Maintenance > what size outboard?
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Thread: what size outboard? Reply to Thread
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Topic Review (Newest First)
05-26-2008 03:07 PM
knormb I forgot to mention that I'd be buying the High Thrust model. Therefore, a few pounds heavier. So you've convinced me. It will be the 9.9, 25" shaft. I'll clean up (and tune up) the Johnson and maybe get a few hundred for it.

No rush though, I'll have to wait until I haul the boat out for the bottom cleaning. In the meantime, guess I'll just sail whenever I can.

thanks again - Sailnet is a great community!

Norm
05-26-2008 12:58 PM
Valiente
Quote:
Originally Posted by knormb View Post
Thanks for the advice. I've been looking around and talking to other boat owners in the area, and have just about decided that I'll go with Yamaha. For the same reasons mentioned - a reliable product with good dealer support.

So now the decisions (besides when).

8HP vs 9.9? The 9.9 is only a few pounds heavier and $300 more expensive. So if either one would easily keep the boat at hull speed (if necessary), I'm wondering what the extra power would do for me. Less strain on the engine (longer life)? 20% more engine displacement, would that mean 20% higher fuel consumption?

20" vs. 25" shaft? I'll need to replace my motor mount either way, so which one would you choose? My logic leads me towards the 25", in that the power head and tilt handle would be more accessible. What would be the downside?

Thanks again for the great advice!

Norm
Your prop configuration is going to mean more than your HP here, in my opinion, as you can't go faster than 5 knots with a displacement hull. You should discuss power curves and prop pitches with other sailors who understand the concepts. Basically, as a sailboat auxiliary O/B, you want to move large chunks of water, which infers a lot of torque. This argues for the 9.9 HP, but they aren't all created equal. I noticed, for instance, that my 9.9 HP Honda BF100 long-shaft moved my Zodiac onto the plane more slowly than my 25 lbs. lighter Mercury 9.9 HP two-stroke short shaft, but that the top speed was better with the Honda once up on the plane (20 knots vs. 18 knots). Conversely, the Honda worked better as a "tow motor" when I needed to lash the Zodiac to the sailboat when the inboard had issues. The Honda was markedly quieter and cleaner burning than the Mercury, but this is generally the case.

You want a nice clean acceleration without cavitating the prop on a sailboat...whereas an outboard for a planing boat should provide "burst" acceleration...sort of the opposite. So discuss with other outboard users and figure out the weight penalties, etc. A lot of people use 5 HPs around here for 4,000-5,000 lb. 24- and 25-footers, like Sharks, but I notice they tend to run them at top speed to get to the start line.

A note on Hondas: "Hard to start" is relative. My 1985 BF100 and my 2008 BF2 (the air-cooled 27 pound four-stroke) have the exact same "habit". When cold, pull the choke out full and give two rapid pulls. Nothing may happen. Then, push the choke in to the half-way point...give a rapid pull and it should start. Let run for 30 seconds before easing the choke in.

The fact that a semi-antique Honda four and a brand-new model respond identically makes me think that this is a "Honda thing" and not some kind of brand-wide flaw. Nonetheless, Yamahas are also hardly ever a bad choice.

Re: shaft length. This again is a function of your tolerance for weight off the stern, your motor lift arrangements, the height of your transom and the likelihood of the prop clearing the water while in a seaway. Generally, long shaft is preferred, but again, find out what works for boats with similar set-ups. I like motor wells in smaller boats, but they aren't common these days.
05-26-2008 12:58 PM
KnightsDream I found the article and comments very interesting and helpful. Thank you for all of the information.
05-26-2008 12:55 PM
Plumper I think you'll find, on the Honda website, that the 8 and the 9.9 are exactly the same engine with some high performance tuning stuff on the 9.9.

Honda BF8 4-Stroke Marine Outboard Engine - 8 HP Motor Specs

Honda BF9.9 4-Stroke Marine Outboard Engine - 9.9 HP Motor Specs

I had a 9.9 and it was fantastic. It always started, ran very efficiently and was powerful and quiet. It pushed my Ranger 26 at hull speed even into nasty winds.
05-26-2008 12:32 PM
Quickstep192
Quote:
Originally Posted by feetup View Post
Quickstep;

Interesting, I just saw 98 lb for the 9.9, and 97 for the 8hp. Both in the high tourque "T" models, not the standard "F". I didn't check the 2 strokes.

Feetup

I was looking at the models they called "portable". When I looked at the "T" models, I saw more similar weights, albeit 102 and 104.

2006 Yamaha High Thrust Specifications


Honda's website shows the current Honda 8 at 92lbs. No wonder it seems so heavy!
05-26-2008 12:18 PM
feetup Quickstep;

Interesting, I just saw 98 lb for the 9.9, and 97 for the 8hp. Both in the high tourque "T" models, not the standard "F". I didn't check the 2 strokes.

Feetup
05-26-2008 12:14 PM
feetup 8 or 9.9? With the weight being the same, the 9.9 seems the better option. Pounding into chop can be a real Hp. sponge. Just because you have more power available doesn't mean you always have to use it. As far as fuel consumption goes, yes, if you are using all the power you have available you will use more fuel for more Hp. There would be very little difference between the two at a specific speed at or below hull speed, and quite possibly the larger rated motor would give you better economy by being throttled down compared to the smaller rated motor. If you look at a fuel consumption/output graph of most engines you will see a rather sharp rise in consumption as the output gets closer to maximum. I see the T9.9 is 212 cc and the T8 is 197cc. The High Thrust version of the T 9.9 is 232 cc, and one pound heavier than the T9.9. Not a lot of difference, same gear ratios, and only one pound different in weight. Personally I would opt for the 9.9 and discipline myself not to use more power than I need at a given time. Less fuel, longer life, and a reserve of power if you find wind, chop and current against you.

As far as shaft length goes, unless you cannot lift the leg out of the water for some reason, the long shaft is the best option. When motoring ahead of short steep seas, it is not uncommon to have the prop come out of the water, or at least close enough to the surface to cavitate. Conversely, it is not unheard of to drown the power head just after the stern squats into the trough. These are probably the two most common arguments against outboards in the old outboard vs. inboard debate on sub 30 foot boats. The long shaft, run a little deeper than normal helps on both accounts.

As far as price goes, it doesn't really look like an issue.

Around my neck of the woods, most of the fishing guides are going with the Yamaha, and every yacht owner I have talked to about the Yamaha has nothing but good to say. One owner of a 25' has the 9.9 new last year and thinks he might have a bit of overkill, but admits he has never been out in nasty weather where he might need all he can get.

My boat has the outboard waaayyy out there, with a reverse transom, and the electric start/remote is almost essential.

Feetup
05-26-2008 11:27 AM
Quickstep192 According to the Yamaha website, the weight difference is 91lbs versus 83lbs. I suspect the weight difference is mostly that the 9.9 has electric start. A quick check of the Yamaha website shows that the 8hp 2 stroke motor is only 60lbs, so at 83 lbs, you're already adding 23 extra pounds. In my case, that makes the boat heavy in the butt. Electric start might be nice, but I think these motor start pretty easily with the yank start.
05-26-2008 10:35 AM
knormb Thanks for the advice. I've been looking around and talking to other boat owners in the area, and have just about decided that I'll go with Yamaha. For the same reasons mentioned - a reliable product with good dealer support.

So now the decisions (besides when).

8HP vs 9.9? The 9.9 is only a few pounds heavier and $300 more expensive. So if either one would easily keep the boat at hull speed (if necessary), I'm wondering what the extra power would do for me. Less strain on the engine (longer life)? 20% more engine displacement, would that mean 20% higher fuel consumption?

20" vs. 25" shaft? I'll need to replace my motor mount either way, so which one would you choose? My logic leads me towards the 25", in that the power head and tilt handle would be more accessible. What would be the downside?

Thanks again for the great advice!

Norm
05-25-2008 09:29 PM
Quickstep192 I would say go with the one that has the best service network available in your area. I swapped an 8hp 2 stroke Yamaha for a 8hp 4 stroke Honda a few years ago. Since then, the local Honda dealer has closed and I find myself having to do my own repairs. I'm OK with that, but my skill level isn't very high. The 4 stroke is definetly more economical on gas. That is slightly offset by the need to do oil changes, but I'll trade that for never having to buy or mess with that stinky 2 stroke oil. My 8hp 4 stroke Honda is quite a bit heavier than the old 2 stroke and makes the boat a little aft heavy, so I had to ballast out the bow. I would imagine that a 9.9 would be heavier yet, but they may have impoved that in the years since I got mine.
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