Suggested Outboard Power

Designs for inboard or outboard power

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NB Boats
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Suggested Outboard Power

Postby NB Boats » Tue Feb 07, 2017 9:20 pm

Would like some suggestions as to power restrictions on the plans for most of the boats. The recommended HP suggestions seem understated. Are they able to increase HP for plans with some minor changes to the hull.......if strengthening the bulkheads? Specifically the Squirt plans state a max power of 10HP. Would like to increase to 20HP.

Regards

Gary

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Re: Suggested Outboard Power

Postby Hercdrvr » Wed Feb 08, 2017 11:00 am

20 hp on a Squirt is perfect. 28 mph with me in it, plenty fast for this little boat.
Matt B
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Lots of fun factor with 20 hp

Hercdrvr
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Re: Suggested Outboard Power

Postby Hercdrvr » Wed Feb 08, 2017 11:04 am

One more thing, sure a 25hp would be nice but way too heavy for a Squirt. 20hp is about 120 lbs, 25 hp jumps to 180lbs

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DrBryanJ
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Re: Suggested Outboard Power

Postby DrBryanJ » Wed Feb 08, 2017 11:05 am

I believe the hp rating is based on the coast guard regs as shown in this page http://newboatbuilders.com/pages/hp.html based on length and width. I know many have overpoweder their boats with success.

I plan to do the same with my malahini.

Bryan
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My wife said "If I build a boat, she's getting a divorce."

BillW
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Re: Suggested Outboard Power

Postby BillW » Wed Feb 08, 2017 11:46 am

This is a very complex, and even controversial, subject. A book could be written. I won't get into all the factors,
and there are many.

I don't think anyone, in this day and age, will suggest that you exceed the maximum horsepower recommended by the US Government.

However: most of the Glen-L boats, including the Squirt, were designed before horsepower ratings existed. Thus, the argument could
be made that these boats were "grandfathered" and exempt from the recommendations. Perhaps that is a very lame argument.
The Glen-L boats are very well designed, but it's up to you, to be sure it is well built. There is an article, written by Mr. Witt in one of the Glen-l
newsletters, on the subject of porpoising (running instability) in small boats.

If you look at the Customer Photo Section, you will see that many Squirt builders used outboards of more than ten horsepower, with
good results, using a "reasonable" size motor. Although, one guy (me) got a little carried away. You can read about our Squirt in the
Boatbuilders Blog section. Go back 2 or 3 previous pages and find Bill & Linda's Squirt.

By the way, if horsepower is doubled, then speed will increase to about 1.3 of what it was.
If power tripled, then speed will be about 1.5 times what it was.
If power 4 times, then speed will be about 1.75 what it was.
If power 6 times, then speed will be about double what it was.
These figures are taken from the Mercury Prop Slip Calculator.

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Bill Edmundson
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Re: Suggested Outboard Power

Postby Bill Edmundson » Wed Feb 08, 2017 12:10 pm

BillW's speed/HP numbers are what I see. My Tahoe will do 40 mph w/125 hp. It would take 250 hp to get to 50 mph.

Bill
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NB Boats
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Re: Suggested Outboard Power

Postby NB Boats » Wed Feb 08, 2017 1:39 pm

Thanks for all the replies gentlemen........the information is very helpful. My concern entirely revolves around what the coat guard regulations are and how to increase to a reasonable HP. For example a 20HP on the squirt. What needs to be done to the plans.........as Bill W points out, many of these boats were deigned prior to the regulations.

Does Glen L have access to the naval architects so that the rating for increased HP can be approved?

Thanks

Gary

NB Boats
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Re: Suggested Outboard Power

Postby NB Boats » Wed Feb 08, 2017 1:48 pm

To add to my last post......I am selling the boats. Therefore restrictions and safety must be followed.

Thanks

Gary

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Re: Suggested Outboard Power

Postby BillW » Wed Feb 08, 2017 2:19 pm

Yes, Bill Edmundson, those numbers assume that progressively larger outboard motors are installed on the same boat.
But of course, in the real world, larger and larger outboards quickly become prohibitive for many reasons, not the least
of which is their weight, and the resulting weight distribution. In that area, vintage outboards, especially Mercurys, have
a large advantage over modern outboards.

Bear in mind, the Max hp recommendations are only for small outboard boats.

In the boat racing world, as in the aircraft world, horsepower alone is not enough for significant speed increase.

Your boat could probably hit 80 with only 750 hp.....

Bill

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hoodman
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Re: Suggested Outboard Power

Postby hoodman » Wed Feb 08, 2017 2:25 pm

The smaller boats feel like they are going faster than they really are.

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Bill Edmundson
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Re: Suggested Outboard Power

Postby Bill Edmundson » Wed Feb 08, 2017 4:57 pm

It is really hard to compare engines. The old outboards were rated at the flywheel. New ones are rated at the prop. All of the old engines were 2 stroke. Most new are 4 stroke. That said, the Squirt is a small boat! Weight on the transom and more hp changes things quickly.

I do not work for Glen-L. Some people think I do. So, I will not endorse a change in recommendations. Some, I might do myself. I won't say it.

I don't think I want 750 HP! :lol:

Bill
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Hercdrvr
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Re: Suggested Outboard Power

Postby Hercdrvr » Fri Feb 10, 2017 3:03 pm

According to the formula Dr Bryan gave us a link for, the Squirt math looks like this

11x 4 x 2 -90 = -2 hp max

Maybe the Squirt is intended for display purposes only

http://newboatbuilders.com/pages/hp.html

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Re: Suggested Outboard Power

Postby Mark-NJ » Fri Feb 10, 2017 4:27 pm

Here's the other thing:

As HP goes up, speed increases a little bit. It's not linear, as shown in the numbers above.

But you should also factor in fuel consumption: burn rate goes up a lot! The cost to go "a wee bit faster" is pretty big!

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Bill Edmundson
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Re: Suggested Outboard Power

Postby Bill Edmundson » Fri Feb 10, 2017 4:57 pm

The way I read the charts with a factor of 44 it's 10 hp.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Hercdrvr
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Re: Suggested Outboard Power

Postby Hercdrvr » Fri Feb 10, 2017 5:47 pm

Your right Bill, I was using the big boy boat formula, my bad sorry.

Matt B


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