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post #11 of 27 Old 06-21-2016 Thread Starter
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Re: Outboards and sailboat balance question

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OP asked if the weight aft might be compensated for with weight elsewhere. No it cannot. The weight needs to be either removed from the boat or moved towards the center. Fuel tanks and batteries might be moved. Crew can sit more forward.
That's the standard point of view. Everyone repeats this as if its gospel, but few people actually try to compensate.

This article suggests that its not entirely the case:

Let Your Weight Work For You | Sailing World
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post #12 of 27 Old 06-21-2016
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Re: Outboards and sailboat balance question

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Originally Posted by Zarathu View Post
Does having an outboard on a small sailboat unbalance the boat and cause pitching?

I was told in another place that having a 90 lb outboard on a 19 foot sailboat would unbalance the boat and cause pitching and hobby horse actions.

I have not noticed this with a 60 pounder and two people at the stern in the cockpit, but again I don't tend to sail in conditions where the wave heights are high enough to cause pitching because my only sailing partner is the admiral, and conditions like that scare her.

Can this be balanced by adding movable ballast forward to the center post or to the bow, or by hiring a 65 pound kid to move around inside the cabin?

Hobby horsing would just be made worse by adding ballast forward. This is why lots of folks agonize about adding more anchor chain to their forward anchor locker.

It's about angular momentum. By trying to "balance" by adding ballast, you'll have more angular momentum. Moreso the further away from the center of mass. This will resistant motion initially, but a wave is going to get that boat bouncing regardless, and now it'll bounce longer (aka, "hobby horse").
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post #13 of 27 Old 06-21-2016
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Re: Outboards and sailboat balance question

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Originally Posted by Zarathu View Post
That's the standard point of view. Everyone repeats this as if its gospel, but few people actually try to compensate.

This article suggests that its not entirely the case:

Let Your Weight Work For You | Sailing World
Yes, momentum works both ways, which is why these things are difficult to get my head around and decide what's better.

For example, if you have weight spread out fore + aft, you'll have more angular momentum on the pitch axis. The boat will be harder to pitch, but once it happens, it'll take longer to damp out that energy.

For a given wave, a boat with the weight spread out fore + aft will pitch to a lower amplitude (height), but will hobby horse longer than the same boat with that weight put in the center. I think.

So if your problem is that you are hobby horsing, one deflection seems to keep you bouncing for longer than you'd like, then centralizing your weight would improve things.

If your problem is that you seem to deflect way too high on impact with a wave, then maybe spreading weight would improve things.

The OP has already /added/ angular momentum by adding a heavier engine on the stern. Adding even more angular momentum will not counteract this.

Last edited by chris95040; 06-21-2016 at 07:40 PM.
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post #14 of 27 Old 06-21-2016
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Re: Outboards and sailboat balance question

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Originally Posted by Zarathu View Post
That's the standard point of view. Everyone repeats this as if its gospel, but few people actually try to compensate.

This article suggests that its not entirely the case:

Let Your Weight Work For You | Sailing World
Like when they write "We want to limit pitching as much as possible. Now we begin squeezing everybody together."

Apparently in light wind they find it advantageous to "tune out" the pitching by moving the weight. Makes some sense if you can find a spot to put the weight where you are "crushing" the waves instead of pitching over them and crashing down the other side. I doubt they ever move as far as leaning back over the transom.

All well and good to move weight around in a dinghy, but not likely to happen with those outboards clamped to the transom and mooring gear forward.

The gospel is largely correct. However like most popular gospels it is completely ignored by many. Especially so ignored by most heavy cruisers who would stand to benefit greatly in added comfort both underway and at anchor.

"...there are two kinds of opinions, those based upon tradition ... and those having something in their favor." B. Russell
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post #15 of 27 Old 06-22-2016 Thread Starter
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Re: Outboards and sailboat balance question

What are the wave conditions that produce hobby horsing? Obviously on a flat lake or other area where the wave height are less than a foot, you are not going to have enough wave action to cause that, no matter what, right?

So what would the conditions have to be? How high would the wave height have to be?
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post #16 of 27 Old 06-22-2016
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Re: Outboards and sailboat balance question

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So what would the conditions have to be? How high would the wave height have to be?
Depends on your boat. I would guess 3-4 foot steep waves will make you miserable, where they wouldn't bother a bigger boat. Meanwhile, you may smoothly ride up and over bigger waves that make a bigger boat slam miserably (but if they are very steep/breaking they will rapidly get dangerous for you).

Moving weight around can dampen the oscillation, and broadly speaking weight in the ends is something to avoid. But if you sail a WWP - even if you're not ready to forgive 1.5 knots of boatspeed - you probably wouldn't worry much about a guest sitting aft with you rather than forward. In the weather you are likely to want to sail in it will not significantly affect boat trim.
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post #17 of 27 Old 06-22-2016
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Re: Outboards and sailboat balance question

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Originally Posted by Zarathu View Post
That's the standard point of view. Everyone repeats this as if its gospel, but few people actually try to compensate.

This article suggests that its not entirely the case:

Let Your Weight Work For You | Sailing World
The reason we care about weight in the ends is that the mass moment of inertia increases as the square of the distance from the center of gravity to the incremental mass (or weight). "Compensating" by "balancing" the weight forward only increases the torque required for a given rotational acceleration which means once moving stopping rotation increases dramatically. In this case we are talking about rotation in the vertical longitudinal plane, or pitch. Weight in the ends increases the extent of pitch and distorts the shape of the acceleration curve with time. That means hobbyhorsing.

The article isn't really relevant to the original question because the weight distribution discussed is dynamic and in direct response to boat motion. Unless you plan to run up and down the deck hugging your outboard it doesn't apply.
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Re: Outboards and sailboat balance question

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Depends on your boat. I would guess 3-4 foot steep waves will make you miserable, where they wouldn't bother a bigger boat. Meanwhile, you may smoothly ride up and over bigger waves that make a bigger boat slam miserably (but if they are very steep/breaking they will rapidly get dangerous for you).
In a little boat like mine, I wouldn't sail in those conditions. And if I had to, worrying about hobby horsing would not be one of my concerns.
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Re: Outboards and sailboat balance question

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Unless you plan to run up and down the deck hugging your outboard it doesn't apply.
I'd like to do that..... but I couldn't run up and down the deck carrying nothing since I don't have a deck.

I fail to understand how the addition of 30 more pounds on the stern would suddenly cause a horrible rocking motion, bad pointing, bad leeward steerage, poor light wind when having two 215 lb adults sitting at the stern, one 60 lb motor, and one 30 lb gas tank did not.

I have to conclude that while the potential is certainly there, those who have experienced it, must sail in waters that are quite different than where I sail.

Of course the information is wonderful to have, and if it turns out to be an issue, I will certainly sit closer to the cabin, stow the 30 lb Torqeedo, and move the gas tank to the central starboard side.

I cannot do anything about the 60 lb motor since that can't be moved, and there are times when I need a motor that big, since I don't have a slip, I have a mooring, and in the event of a hurricane, I need to get the boat out of the water to launching 6 miles away, while pulling a dinghy, against the tide and wind in Murphy's Law rough seas(or 12 miles south to a safe harbor in worse conditions on the ocean).

Thanks for your help.
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Re: Outboards and sailboat balance question

Z I want to see your boat! Do you have any photos posted?

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