Motor Weight?

Outboard designs up to 14'

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weasel
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Location: Clear Lake, MN
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Motor Weight?

Postby weasel » Wed Dec 21, 2016 5:08 pm

My Tunnel Mite is almost ready for fiberglass and paint. I just got the motor all rebuilt/painted/new stickers looks new. It's a 30hp Yamaha, 3 cylinder, short shaft, and weighs 135lbs. It is a little heavier (25lbs) than recommended. I did beef up the transom boards to 1/2" instead of the 1/4" and lengthen & widened the motor board braces and made the motor board itself thicker (2" now) than recommended too. I've seen 25 hp long shafts on these tunnel mites and I've seen 40's on the TNT that boat is only "slightly" bigger. Anyone put a motor like this on a tunnel mite and have any experience? Thanks and a MERRY X-MAS too :D !!

JimmY
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Location: Brighton, MI

Re: Motor Weight?

Postby JimmY » Fri Dec 23, 2016 10:06 am

Hi Weasel,

It sounds like you've beefed up the transom enough, so I don't think you will have problems there. My concern is that the Tunnel Mite is a twin sponson hull where the TNT is typical planing hull. So, while they are similar in length, they are different beasts. The Tunnel Mite will have support (float) the extra weight on a smaller volume until the flat hull between the sponsons is in the water. You may have to be careful coming off plane to make sure you don't get swamped over the transom.

My friend has a 10" fiberglass hydro with a 10hp Evinrude. When we put on my 18hp Johnson to check it out, you could see it sitting lower in the water and it was dicey coming off the plane as the wake caught up to it.

I would try to research the weights of the 25hp's you've seen, and see if you are significantly over them. Also, your hull weight and your weight may come into play here as well. The webpage says power up to 100lbs, so you are 35 lbs. over the design. Please post your experience.

I am not an naval architect, nor do I play one on TV, you mileage may vary, always wear a life jacket and a helmet.

Merry Christmas,
-Jim
Nothing says poor craftsmanship like wrinkles in your duct tape!

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chugalug
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Location: top of mn.

Re: Motor Weight?

Postby chugalug » Sat Dec 24, 2016 9:56 pm

:roll: Do you plan on installing any flotation?.Don't turn it into a sub.and ditto on the lifejacket.
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine

jplatou
Posts: 38
Joined: Fri Nov 27, 2015 6:43 pm

Re: Motor Weight?

Postby jplatou » Sun Dec 25, 2016 7:05 pm

I have not build the Tunnel Mite, but have a lot of experience.

You are not only 35 pounds over weight but 35 percent over the allowable limit.

I can tell you weight distribution, is most important on any boat especially the smaller ones such as the Tunnel Mite. A lot depends on your skill level and the location of all other loads in the hull. I have first hand experience moving the 3 gal fuel tank form the transom to under the deck in my grandson's 8' mono hull hydro with just a 6 HP, the fuel tank full was only 35 pounds but made a huge difference. The difference in performance and handling between my 60 pound grandson and my 190 pound self were also an eye opener!

I did lean over the engine (79#) of the same 8' hydro and the next second was swimming as the boat sunk in 3 ft of water!

I have conservatively 12,000 operating hours in boats from 8 to 40 feet. I would probably try it, but would not recommend it.

A submerged bare wooden hull will support about half its weight without flotation. If you hull weight is 100 pounds, it should support 50 pounds or so, you engine is 135 pounds, you need additional floatation!

weasel
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Location: Clear Lake, MN
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Re: Motor Weight?

Postby weasel » Tue Dec 27, 2016 9:25 pm

Hello People!

Thanks for some of the input and I always like more. This Tunnel Mite is 10' long, so that's 2 feet longer than the 8' one talked about. I don't know if that 2 feet makes a big diff or not. I found out he motor is 130lbs has electric start, I have a small marine battery in the rear too. I am adding floatation foam in the middle and forward sections. It doesn't help it float any better, until it's submerged of course. I also can get my hands on a 25 horse Yamaha that weighs 120#. I might try the bigger one in shallow water to see how it floats first, if it's too low I will have to trade it in for the 25. But if it floats okay, it will fly across the lake for sure. So any more advice is always welcome and happy boating everybody!!

jplatou
Posts: 38
Joined: Fri Nov 27, 2015 6:43 pm

Re: Motor Weight?

Postby jplatou » Thu Dec 29, 2016 6:47 pm

Check the weight of the battery! Could be 40 plus pounds, a lawn mower battery is much lighter, I use one on my 2006 25 Merc 4 stroke (165#).

Also putting battery forward will be better, actually a battery forward will offset the extra weight on back.

weasel
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Location: Clear Lake, MN
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Re: Motor Weight?

Postby weasel » Sat Dec 31, 2016 4:38 pm

Hello "JPLATOU" I have just a small wet bike battery 320 CCA (5 1/8" x 7") not much weight 5-8lbs. The boat dealer says that will be plenty to start it. I have no room to put it up front with my feet/throttle/steering wheel all there. I would have to cut a door or something on the main hood bow cover and put it under the hood/bow to get it up front, so I can get it in and out. I don't want to do that I want a nice decal on the hood/bow. Do you have the same tunnel mite boat, and it can handle 165# motor?

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Roberta
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Location: East Troy, Wisconsin

Re: Motor Weight?

Postby Roberta » Sat Dec 31, 2016 5:42 pm

For a lighter battery, check out some of the Odyssey batteries. I used them in all my boats and airplanes.

http://www.odysseybattery.com/

The PC680 was used to start my Lycoming 0-360 airplane engine

Roberta :D
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".


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