Suggested Outboard Power

Designs for inboard or outboard power

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Re: Suggested Outboard Power

Postby Hercdrvr » Fri Feb 10, 2017 5:55 pm

I was plugging some numbers into these formulas and can't figure out how a 19' Bass boat hangs a 225hp back there. I've ridden in my friends Stratos bass boat and it's scary to ride in at 65 mph.

Speed over 35mph is way overrated, uncomfortable and expensive anyway.

Matt B

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Andy Garrett
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Re: Suggested Outboard Power

Postby Andy Garrett » Sun Feb 12, 2017 8:44 am

Bear in mind, these are just recommendations. No one is going to give you a ticket for having too much motor on your boat.

The Coast Guard is suggesting a starting point based on assumptions. The idea is to ensure that your boat can maneuver safely. It has almost nothing to do with speed (a Zip and a Cracker Box are about the same length and width but have vastly different performance envelopes).
What the Coast Guard doesn't know is how much you hull weighs and how that weight is distributed. They don't know if you have a fin, a skeg, multiple skegs, or strakes. Again, its just a broad recommendation.

I run a 2-stroke 50HP on a Zip rated for 40HP. I have a single 48" skeg designed like an air foil terminating 30 inches from the transom. My fuel tank is located in the bow and my battery is aft. These specifications make my boat unique among Zips as each of our handmade boats is. I'm pretty certain that if I made a max turn as fast as I could spin the wheel at full throttle, I could significantly loose control and maybe even roll it in rough water. Some Zips might give up control sooner than mine--others, not at all.

Because I am overpowered, and because my engine is 40 years old, I tend to baby my boat. Such turns just don't happen. On choppy Kansas and Oklahoma lakes, I seldom run full throttle.

More than anything, it's about efficiency. Why burn twice as much fuel to gain 2mph? I only run a 50 because that's what came on the donor boat. If it had been a 30, that's what would be hanging on the transom.

As previously stated, books could be written about all the variables. It's not as simple as X+Y = Z. Do your own testing using the Coast Guard recommendations as a good place to start.
Andy Garrett

Perhaps the slowest Zip build in Glen-L history...

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Re: Suggested Outboard Power

Postby Scott » Fri Feb 24, 2017 4:08 pm

Yamaha recently introduced a new 25hp 4 stroke similar to their 25hp and Mercs 25hp 2 stroke weight at 126 lbs weight. Pretty amazing. But yes the expense would throw off the purpose.

Older ratings are flywheel rated as well. When was the conversion to propshaft hp? Somewhere in the 80's?

A flash of lightning with a simultaneous crash of thunder.

An ignition system of early Mercury outboards that not only is a nightmare to diagnose but also improves a marine mechanics competency.

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