Laguna Madre 18 with tunnel

Power Boats only. Please include the boat type in your question.
User avatar
cape man
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8268
Joined: Sun Jan 20, 2008 12:02 pm
Location: Lithia, Florida

Laguna Madre 18 with tunnel

Post by cape man »

There was another thread concerning this, but I'm going to start another as that one got messy...

Has anyone built an LM18 with a tunnel and if so are there any performance reports? Of most interest is draft underway and getting up on plane. Is 6" for both possible? There's a new builder considering it, and I have an LM 18 hull that I'm going to finish and thinking about a tunnel version.
The world always seems brighter when you've just made something that wasn't there before - Neil Gaiman

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: Laguna Madre 18 with tunnel

Post by TomW1 »

cape man did a search for you trying to be a help. There were 159 pages only one was completed and it did not have a tunnel. He was polling in 6" of water. Though he had a jack plate. He did not give many specs. There are builds, in both this section, and both the Builders sections. Just do a search for the LM18. Good luck guy.

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

Cbuf
Active Poster
Active Poster
Posts: 356
Joined: Sat Mar 30, 2019 10:38 pm
Location: Wisconsin

Re: Laguna Madre 18 with tunnel

Post by Cbuf »

I don't think the completed build threads is maintained any more. I finished mine over year ago, but they never moved it to completed. As for the running draft, if you keep the boat light, and not throw a 50 Hp on it I would think a running 6 would be achievable with a tunnel. I have hit a sandbar in mine that was about 8-10" deep when running. The boat didn't hit just he prop. I have a 50hp so the lower unit is bigger than say a 30 hp . The 2" tunnel, a 30 hp, and a light load should get you about there.

cbuf
See my LM 18 build here.
viewtopic.php?t=64254
See my LM 18 Questions here.
viewtopic.php?f=2&t=64299&hilit=lm18\
Finished Boat Here
viewtopic.php?f=25&t=65173

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: Laguna Madre 18 with tunnel

Post by TomW1 »

Cbuf wrote: Mon Apr 12, 2021 9:25 am I don't think the completed build threads is maintained any more. I finished mine over year ago, but they never moved it to completed. As for the running draft, if you keep the boat light, and not throw a 50 Hp on it I would think a running 6 would be achievable with a tunnel. I have hit a sandbar in mine that was about 8-10" deep when running. The boat didn't hit just he prop. I have a 50hp so the lower unit is bigger than say a 30 hp . The 2" tunnel, a 30 hp, and a light load should get you about there.

cbuf
cbuf you have to move pictures and specs that you want down to the Finished Boats section it is not automatically done.

Tom
Last edited by TomW1 on Mon Apr 12, 2021 10:46 pm, edited 1 time in total.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

wwsmith
Frequent Poster
Frequent Poster
Posts: 101
Joined: Tue May 05, 2020 6:52 pm
Location: Texas

Re: Laguna Madre 18 with tunnel

Post by wwsmith »

My LM 18 does not have a tunnel, but at rest, its about a 6" draft depending on how everything is balanced (there in a 13 gallon fuel tank in the front compartment), and how many are on board (usually 2 adults and a child). I'd estimate draft while running to be 3". Lately we've been fishing really shallow and I hit sandbar often.

User avatar
cape man
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8268
Joined: Sun Jan 20, 2008 12:02 pm
Location: Lithia, Florida

Re: Laguna Madre 18 with tunnel

Post by cape man »

Are you running a jack plate? Never mind, I just looked at your thread and there's no jack plate involved.
The world always seems brighter when you've just made something that wasn't there before - Neil Gaiman

Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8920
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: Laguna Madre 18 with tunnel

Post by Fuzz »

Just wondering for those with a tunnel in one what happens when you tag bottom? Do you wipe out the prop or is it high enough to be protected?

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: Laguna Madre 18 with tunnel

Post by TomW1 »

Guys lets get real on how a tunnel works and what the capabilities of it is. First Fuss, if the bottom hits the prop may or may not hit. It depends on how far the prop is raised up into the water coming out of the tunnel. The tunnel creates a hump of water out as speed builds up and depending on design can be 4-8" in height. You start the motor down at the normal bottom and as speed increases raise into the the hump coming out of the tunnel. Watch your temp guage and if needed you may need to lower your motor a little as the water pickup is not getting enough to cool it.

Lets look at props that would work for 30-40HP motors. The diameters are from 10" for 30HP to 11.25" for 40HP so if the hump is 6" you will not have any part of the prop hanging below the boat once on plane and the prop raised. You will have to ask Jacques what the hump is for the LM18.

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

Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8920
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: Laguna Madre 18 with tunnel

Post by Fuzz »

I understand how a tunnel works. What I was asking is will the tunnel on a LM let you raise the motor enough that you hit bottom with something other than the prop. Where I would use one is gravel bottom so hitting with the prop will tear it up. And being as the water is glacier fed it is very murky making depth hard to read.

Browndog
* Bateau Builder *
* Bateau Builder *
Posts: 1243
Joined: Sat Jun 04, 2016 7:38 am
Location: Shellman Bluff, GA

Re: Laguna Madre 18 with tunnel

Post by Browndog »

The most exciting boat ride in rocky waters I was ever in was an Aluminum Shotover jet boat in Queenstown, New Zealand.

The boats were used as excursion boats and were powerful, fast and we went through some skinny water that I couldn’t believe in glacier fed rocky rivers with very little room for error. Impressive boats and very impressive operators.

Post Reply

Who is online

Users browsing this forum: No registered users and 6 guests