Shortened LM18

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NaplesEuroTech728
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Shortened LM18

Post by NaplesEuroTech728 »

Hi all!

I'm new here but have been browsing plans and kits here for years since the days of bateau.com

I'm finally to the point of getting ready to pull the trigger and love the LM18 for its draft and wide beam than the FS18 that I've always loved but I'm limited to 20hp and a smaller storage space so I'd like to scale it down 10% shorter without changing the beam.

Will this horribly affect performance and handling? And would i have to have the plans resized professionally to maintain hull proportions?

Thanks for any input,
Alexa



TomW1
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Re: Shortened LM18

Post by TomW1 »

Welcome Alexa. If you scale in one direction you should scale in all derections. While a 20HP is on the lower end of the recommend motors for the LM18 it will still propel you well. Depending on the weight as you leave the dock at 1250lbs you will have a top speed in the low mid 20's, 23-25. A 30 give speeds in the upper 20's. So I think you will be fine with a 20 if you are not a speed demon. :D Or over load the boat.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Reid
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Re: Shortened LM18

Post by Reid »

NaplesEuroTech728 wrote: Tue Nov 09, 2021 7:19 pm Hi all!

I'm new here but have been browsing plans and kits here for years since the days of bateau.com

I'm finally to the point of getting ready to pull the trigger and love the LM18 for its draft and wide beam than the FS18 that I've always loved but I'm limited to 20hp and a smaller storage space so I'd like to scale it down 10% shorter without changing the beam.

Will this horribly affect performance and handling? And would i have to have the plans resized professionally to maintain hull proportions?

Thanks for any input,
Alexa
Welcome to the Forum!
As TomW1 suggests, you must scale in all directions. However, as far as the ability to scale the LM18, Jacques (designer) will have to be the one to ultimately approve this as a viable solution.
To offer another solution, have you taken a look at the FS14_LS. I know it is shorter than you may be considering but I think it is work a look considering your need for a shallow draft, sturdy skiff. The FS14 has a 60" beam, shallow draft, and is ideal for a 20 HP outboard.
Here are the study plans: https://www.boatbuildercentral.com/Stud ... STUDY.pdf

Best of luck!
-Reid
Someone asked me, if I were stranded on a desert island what book would I bring... "How to Build a Boat."
- Steven Wright

NaplesEuroTech728
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Re: Shortened LM18

Post by NaplesEuroTech728 »

Reid,
Thank you for your input. I have looked at it and teeter tottered back and forth. My only concern with the fs14-ls is that i commonly fish with my wife and I'm concerned about the space with 2 anglers

NaplesEuroTech728
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Re: Shortened LM18

Post by NaplesEuroTech728 »

Tom,
That's great to know. I'm a little bit of a speed demon but right now I have a 16 foot jet boat that i plan on keeping so I have my need for speed filled, however it's miserable even in 1.5 feet of water

Thank you,
Alexa

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Re: Shortened LM18

Post by Reid »

NaplesEuroTech728 wrote: Wed Nov 10, 2021 10:24 am Reid,
Thank you for your input. I have looked at it and teeter tottered back and forth. My only concern with the fs14-ls is that i commonly fish with my wife and I'm concerned about the space with 2 anglers
We have an FS14_LS sitting here in our shop (built by SeaSlug). I can tell you that two anglers is not an issue at all. Three is pushing it, however, on the FS14_LS.
-Reid
Someone asked me, if I were stranded on a desert island what book would I bring... "How to Build a Boat."
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VT_Jeff
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Re: Shortened LM18

Post by VT_Jeff »

I upscaled the FS14LS by 10%, run it with a 20hp and fish with my wife aboard 90% of the time, often with our dog. Works great. Link in my signature.
There are only two seasons in Vermont: boating season, and boat-building season.

Completed Paul Butler 14' Clark Fork Drifter
Completed Jacques Mertens FS14LS + 10%, Build Thread
Started Iain Oughtred Tammie Norrie

NaplesEuroTech728
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Re: Shortened LM18

Post by NaplesEuroTech728 »

Jeff,
I will definitely check it out! Somehow in all the discussion of scaling that option never crossed my mind. Oops
Thank you!

Reid,
Three anglers is not an option within my patience level lol. That sounds perfect

NaplesEuroTech728
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Re: Shortened LM18

Post by NaplesEuroTech728 »

Jeff,
I love your boat and the sizing of it

How did you go about scaling it up?

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VT_Jeff
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Re: Shortened LM18

Post by VT_Jeff »

NaplesEuroTech728 wrote: Wed Nov 10, 2021 5:18 pm Jeff,
I love your boat and the sizing of it

How did you go about scaling it up?

Thanks! It's a great little boat: carries the two of us with ease but is small enough to paddle like a SUP when called for. I should have moved my B frame forward so my client-wife has more foot room, or else made my console vertical instead of swept, which would have reduced my footroom very slightly but increased hers quite a bit(though this would move weight rear-ward, so maybe not)

The scaling is pretty simple: go through each measurement on the plans, add 10%, cross off the old measurement and write in the new one. To easily calc the 10%, I created a spreadsheet that let me enter the inches, 1/2 inches, 1/4 inches and 1/8 inches and it would output the new measurement in inches, 1/2, 1/4, 1/8 etc.

So if I input 20 3/8, I'd get 27 3/4 output.

It's a bit slow, but effective.

Don't scale the transom height!
There are only two seasons in Vermont: boating season, and boat-building season.

Completed Paul Butler 14' Clark Fork Drifter
Completed Jacques Mertens FS14LS + 10%, Build Thread
Started Iain Oughtred Tammie Norrie

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