Tunnel for LM18

[Ryan]

Hey all, I’ve been combing the forums and can’t find where anyone has built the LM18 with the tunnel? Seriously entertaining this before I get any further in my build…. Any thoughts? Probably going to be repurposing a 40hp Yamaha 2stroke(tiller) on a micro jackplate, with trim tabs. I’ve been looking at those compression plates - on the cavitation plate - that many of the tunnel hull guys run in the gulf, thinking that might be an efficient option if I decide to go this tunnel route?

~Ryan

[cape man]

You'll be the first if you build the tunnel version. Jacques partially designed the LM18 to be wide enough (versus the FS18) to add a tunnel, but due to its already shallow draft and the loss of performance a tunnel adds, no one has made one...yet.

The 40, 2 stroke will more than compensate for the performance drop. Go for it!

[Ryan]

I think I’m going to! Originally I really wanted a tunnel hull (prior to buying the plans) I realize the pros and cons. A little nervous to be the Guinea pig. Lol. Never quite seen a tunnel designed like that, it does make sense though -tapers up to 2-7/8 then back down to 1-3/4 similar to an air foil, I’m assuming this is to get the water to speed back up…

[Cbuf]

What is the weight of the 40 stroke? I have a 50 on my LM18 same weight as a 40 in the 4 stroke world. It does change the attitude of the boat at rest. understanding that the tunnel will drop the tail in the water even more plan to add batteries and gas in the front to balance. For me the added weight forced me to go up 2 or 3 holes in the mounting of the motor, so having a jack plate will be key. Plus it will be good because the gear box on the 40 is much bigger than the 30's. I say go for it, I kinda wish I would have. Also, I raised my sole 1", if I were to do it again I would raise it 1.5 inches for proper drainage with more weight, as I run heavy, trolling motor+ batteries, 250 lbs 50HP, 18 gallon livewell, 9 gallon gas tank, etc.

cbuf

[Ryan]

Good info cbuf. I’m trying to keep it light, but jackplate, trim tabs, 12v trolling motor, 10-12 fuel tank, etc. not going to get fancy with a bunch of hatches. Hopefully this will save weight! That 40 2stroke is roughly 190lbs. I’m about 98% certain I’m committing to the tunnel! I will keep in mind raising the sole slightly. I’ll keep everyone updated, some more cutting when I get off work. Hopefully this Christmas break will give me some time to get some good progress done.

[TomW1]

ryan looking good. just follow the build and attachment instrutions for the tunnel and you will be fine. If you have a 90 2st you are saving 20 to 30lbs over a 4st based on Yamaha specs. Adding batteries, gas and trolling motor forward will offset your offset the weight added at the rear. Your build is on track

Keep the good work up. Tom

[Dr Pete]

Here’s your LM18 with tunnel. Port Aransas ,Tx

[Dr Pete]

Sorry the pics flipped. Jacques designed the Lm18 after taking some lines off a skiff built here at. Farley. This particular build has dropped the sheer some. The tunnel was built making parallel cuts on the hull bottom from the stern towards the bow. Notched the transom and then bent this “slot” to join at 6” depth. Builder has expert knowledge and assistance so did not post the build to this forum. I am sure the builder would entertain questions. Merry Christmas to all

[TomW1]

Dr Pete thea is a nice looking LM18, a small console, jack plate and alll Very, very nice. Do you know how much he reduced the sheer by?

Tom

[Dr Pete]

Sheer was reduced May be 2” midship. Towards the bow it was tapered up to near original line. At the stern an inch to inch and a quarter