Everthing I know about outboards. - Page 2 - SailNet Community
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post #11 of 37 Old 04-01-2010
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Dog-

So how do we choose the right prop for our outboards? I have the Honda 9.9 4-stroke (yes, I know it's overkill, but it's new and came with the boat). I hope this isn't a hijack as the info may help the OP as well.

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post #12 of 37 Old 04-01-2010
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You have to just look for a high Thrust Prop that fits your brand

There will NOT be a lot of picks BUT i am sure they make it as i have seen it on a Honda at my marina

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post #13 of 37 Old 04-01-2010
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I'd recommend trying a Pirahna Prop composite prop. They have a blade exchange program if you're not getting the performance you're looking for. You do need a tachometer to really do this right, as you need to see what the WOT RPMs are at...

Pick the wrong prop and you can easily over rev the engine, which is bad. Pick the wrong prop in the other direction, you can easily over prop the engine, limiting your WOT RPM to too low a speed and damage the engine by lugging it.

I would add a tach and see what your WOT RPMs are and what your SOG is and go from there. Ideally, the engine should be propped so that you're in the middle or slightly below the middle of the WOT recommended range, and that you're making hull speed at that point in time.

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Dog-

So how do we choose the right prop for our outboards? I have the Honda 9.9 4-stroke (yes, I know it's overkill, but it's new and came with the boat). I hope this isn't a hijack as the info may help the OP as well.

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post #14 of 37 Old 04-01-2010
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Hm..ok. I have a dwell/tach that I should be able to connect. I'll need a GPS to get my speed though.

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post #15 of 37 Old 04-01-2010 Thread Starter
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I would point out that what is more important than HP is having the right prop. Most of these outboards come with a prop that is better suited to moving a light aluminum jonboat at higher speeds rather than the higher power, lower speed prop a sailboat needs.

Getting the right prop, so you can use the engine at WOT and have the power you need to keep the boat at "cruising" speed is essential.

How much does your boat displace? The typical rule of thumb is 1 HP / 500 lbs. of boat or so. I doubt your boat is 5000 lbs, so 9.9 is probably too much HP for it.
The boat displaces 3100 pounds. We generally have it pretty heavily loaded with two of us and two dogs. We carry food, water, spares, tools, an extra gas can, etc.

I have On a 40 mile motoring day, we averaged better than 5 knots by GPS, not bad for a boat with a hull spped less than 6 knots.

I want to want the Sail pro. I don't get why it won't push my boat better than an old 2 stroke. I get that the power delivery is different, but it seems to me 6hp is 6hp. And, factor into acount the longer shaft, and the high thrust prop, it should push it better.

It's light, cheap, and has a charging system.

I am sure it would work for occasional use, and docking. We rarely day sail- much more frequently out for 1-7 nights. That often puts us in places we need to motor out of. Sometimes all day.

From what I have read those who have it consider it to push much less than a 6hp two stroke. While I have gotten by fine with that amount of power, I don't want to upgrade to less power.

Also- it is reported as having a lot of vibration. Unfortunately, I don't know whether that is compared to an old two stroke, or a new 2 cylinder 4 stroke.

I am trying to get out of buying an over sized, over priced motor, and started this thread in the hopes that somebody would have a great idea. Appreciate all the input.

HH
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post #16 of 37 Old 04-01-2010
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Huh?

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I would just go with the 6hp tohatsu sail pro. It will vibrate, but it will get you to hull speed. I am pretty confident that a T22 does not take much to get moving.

Interestingly the 4hp Tohatsu is the same engine as the 6hp with a different carb, shorter leg, no charging system, and a different prop.

If you can, get the "elephant ear" prop from internet outboards. I have heard bad things about both internet outboards and online outboards, so take your pick!
What did you hear bad about us and where? Our record is 100% spotless with Tohatsu.

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post #17 of 37 Old 04-02-2010
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Quote:
Originally Posted by sailingdog View Post
I would point out that what is more important than HP is having the right prop. Most of these outboards come with a prop that is better suited to moving a light aluminum jonboat at higher speeds rather than the higher power, lower speed prop a sailboat needs.

Getting the right prop, so you can use the engine at WOT and have the power you need to keep the boat at "cruising" speed is essential.

How much does your boat displace? The typical rule of thumb is 1 HP / 500 lbs. of boat or so. I doubt your boat is 5000 lbs, so 9.9 is probably too much HP for it.
Don't Buy It!
Sailingdog is absolutely correct, 8+ hp is way way too much hp, but hp is not the problem, it's the weight. Heavy astern is SLOW.
My Cape Dory 25 weighs 4000# With an 8 hp Honda I get hull speed (gps)
at less than 1/2 throttle, and any more throttle pushes the boat deeper in the water.
You need a 4-6 hp long shaft with a 6" pitch. I repeat: 6" pitch.
Dick
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post #18 of 37 Old 04-02-2010
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I recently sailed on an Antrim 27 that had a Tohatsu. It had a higher pitch sound to it than my Honda but it was smaller, lighter and really moved the boat.

I really think I'd like to step down to something just a little smaller because I can't lock the Honda in the "up" position because it's too big.

What I can't figure out is how to make an honest swap with someone, so that I get a GOOD, slightly used, running engine for my boat. My luck is so poor, that I'll trade away my nearly-new Honda for a junker that repeatedly breaks down.

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post #19 of 37 Old 04-02-2010
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Just thought I'd add my 2 cents for all its worth. I have a 7.5 Tanzer with a Mercury 9.8 ( or 9.9, can't remember ? ) 2 stroke long shaft with electric start with the stock prop. I never run it @ WOT, as the difference half throttle 4 knots to WOT being 5-6 knots , but the fuel economy goes WAY WAY down at WOT. I usually have 4 deep cycle batteries on board, so the 20 minutes or so it takes to get out into the lake, the actual motor charging the batteries is minimal at best. Hope this helps !

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post #20 of 37 Old 04-02-2010
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Tohatsu 9.8 on Catalina 25

I have the Tohatsu 9.8 XXL shaft electric start on my Catalina 25. I got the 7 inch pitch prop. This motor has been flawless for 2 years. I have at times motored for 15 hours in one day. I get around 10 nmpg at 5 knots. Charging circuit works good and I'm pretty much independant of shore power with that and a couple of solar panels. I have probably 300 hours on the motor with zero problems.

I had the Honda 8 before and this motor is quieter, better mpg, more reliable (the Honda was always fouling the idle jet).

Love the electric start. Love the XXL shaft.

It is very heavy, though.

Usually cruise at 5 knots with the throttle just above idle.

My friend has the Mercury 6 HP Long shaft on his Cat 25. Works well, the shorter shaft is an issue and the motor vibrates more.
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