LM 18 First Time Build

Power Boats only. Please include the boat type in your question.
Colemanfire
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Re: LM 18 First Time Build

Post by Colemanfire » Wed Jan 10, 2018 10:04 am

Wow now I'm really confused on what size engine.....

Right now I'm looking for a used 30 to 40hp engine for the boat. I will have some long runs on certain days, depending on where I chose to fish.
most of the engines that I have called on nobody seems to know weights. this is where I wish I was not the genie pig on this boat, I will be basing my final decision mostly on the comments I read here, because I have no experience in this area, I will say that I don't want to under power the boat, I would like to be able to run the boat at a max speed of 30MPH. is this a realistic goal to have and still have the boat perform in shallow water polling? Most of the motors in my price range have been Yamaha and Mercs. Is there some place I can look up weights of the older engines on the web say 2000 to 2008 year?

John



Spokaloo
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Re: LM 18 First Time Build

Post by Spokaloo » Wed Jan 10, 2018 11:23 am

John, if you get a good estimate of the EXACT all up weight of your boat, it's relatively easy to calculate the top speed for a given hp.

Thus, get all your gear weights, what you will carry on the boat, what you and all of your passengers weigh, and add that to the hull weight of the boat. Don't forget things like outboard brackets too. Then one of us can push it through an equation to see what number of horsepower are required to move your given amount of weight. It's simple, and usually effective to within 2-3 mph if you have accurate weights.

E

silentneko
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Re: LM 18 First Time Build

Post by silentneko » Wed Jan 10, 2018 11:33 am

I think KBB lists the outboard weights still. I'd advise you to look carefully at it for the 30-40hp motors, because that's usually the breakover for weight class.

For example many 25 and 30hp use the same blocks and weigh about the same, but a 40hp may use the same block as a 50 and 60hp, meaning for 10hp more you will gain a ton of weight. It's a basic cost benefit analysis to see if the speed is enough to warrant the weight.
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe.....FS17 coming soon!

Mc_Fly
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Re: LM 18 First Time Build

Post by Mc_Fly » Wed Jan 10, 2018 12:42 pm

That’s what made my choice the Yamaha F25. 126lb or 135 for electric start and 20” shaft. Went and eyed one today. Literally the same size as the merc 9.9.

Jeff
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Re: LM 18 First Time Build

Post by Jeff » Wed Jan 10, 2018 12:50 pm

I would really like to hear what quote you received on the new Yamaha 25. We have priced it here on the Treasure Coast of Florida but so far the suppliers do not have any in stock!! Jeff

Marshall Moser
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Re: LM 18 First Time Build

Post by Marshall Moser » Wed Jan 10, 2018 1:33 pm

swglenn wrote:
Sun Jan 07, 2018 10:49 am
Tohatsu has a new 4 stroke 40/50 HP motor that starts at 209#
I'd put this as ideal for this boat heavily laden.

K2FS18
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Re: LM 18 First Time Build

Post by K2FS18 » Wed Jan 10, 2018 4:38 pm

I have the new Yamaha 25 on my FS18. It was topping out about 28 mph with the stock aluminum prop. I repropped with a SS 4 blade to by able to run jack plate up as high as possible. Now it tops at 24mph +/-, but the centerline of the lower unit is up about 4" from bottom of transom. I don't think I really over built my FS18, but some said it weighed a lot, but that was fully rigged. About 440#'s if I remember with everything but the motor and fuel.

I am sure if I propped for speed I could push 30mph plus, but running shallow and popping up on plane where my goals.

Mc_Fly
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Re: LM 18 First Time Build

Post by Mc_Fly » Wed Jan 10, 2018 8:20 pm

Jeff wrote:
Wed Jan 10, 2018 12:50 pm
I would really like to hear what quote you received on the new Yamaha 25. We have priced it here on the Treasure Coast of Florida but so far the suppliers do not have any in stock!! Jeff
Getting mine at dealer cost from a friend. The price for this one today was 3540 plus tax for short shaft electric start. Boathouse marine on beach blvd in jax, fl.

Mc_Fly
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Re: LM 18 First Time Build

Post by Mc_Fly » Wed Jan 10, 2018 8:22 pm

K2FS18 wrote:
Wed Jan 10, 2018 4:38 pm
I have the new Yamaha 25 on my FS18. It was topping out about 28 mph with the stock aluminum prop. I repropped with a SS 4 blade to by able to run jack plate up as high as possible. Now it tops at 24mph +/-, but the centerline of the lower unit is up about 4" from bottom of transom. I don't think I really over built my FS18, but some said it weighed a lot, but that was fully rigged. About 440#'s if I remember with everything but the motor and fuel.

I am sure if I propped for speed I could push 30mph plus, but running shallow and popping up on plane where my goals.
I'm hoping for 22-25mph with the lm18

Jeff
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Re: LM 18 First Time Build

Post by Jeff » Wed Jan 10, 2018 8:42 pm

Mc_Fly, that is a great price!! I have not found one anywhere less than $4,200!! Jeff

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