XF20 or OD18 Mods

Ask questions before buying our plans or request a new design. Anybody can post here
Steven
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 3148
Joined: Thu Aug 22, 2002 1:00 am
Location: Burleson Texas

Re: XF20 or OD18 Mods

Post by Steven »

Those are extremely common on the Texas Coast. A design like that with 2 sheer options would sell very well IMO. Low sheer for flats fishing, and moderate sheer for large lake, near shore activities. I'd build one. ;)

User avatar
sds
Very Active Poster
Very Active Poster
Posts: 525
Joined: Fri Jun 20, 2003 1:00 am
Location: so cal

Re: XF20 or OD18 Mods

Post by sds »

Maybe Jacques could design a version that isn't quite so f-ugly as that.

How's it go? Ugly boats: not worth building.

Maybe it's just a bad angle?

jacquesmm
Site Admin
Site Admin
Posts: 28215
Joined: Wed Aug 14, 2002 1:00 am
Location: Florida USA
Contact:

Re: XF20 or OD18 Mods

Post by jacquesmm »

I would design it if it was more efficient than the boats we have now but those boats have more draft and run a lower prop than our XF20.
See the XF20 study plans, I explain why a Texas scooter style boat must have a deeper draft:
http://www.bateau.com/studyplans/XF20_study.htm
It's in the middle of the page.
It is simple physics, there is no way around it. Whatever people say, you can't go around the math.
The TX18 was designed for exactly that program. It floats in less water than any cat/tunnel type boat and it runs smoother.
Several builders asked for a Texas style tunnel boat and the best way to handle the program is the TX18.

The prop depth is the same when you compare the TX18 to a tunnel boat.

I did contract work for a company that produced such a boat: tunnel cat for flats fishing. The owner did spend a lot of $ testing all kind of tunnel configurations and none worked well.
We tried every possible shape of tunnel but with a single engine, the water in the tunnel was always turbulent and we had to run the prop lower than on a monohull.
He went bankrupt but the molds are still around. About once every two years, a new company buys the molds and advertise the boat as a miracle shallow draft hull. They sell a couple, go under and another guy buys the molds, advertise etc.

If you want less running draft, go the XF20 route. Lift the water with a well designed pocket drive.

Or then, keep it simple and build a PH18.
Jacques Mertens - Designer
http://boatbuildercentral.com

User avatar
sds
Very Active Poster
Very Active Poster
Posts: 525
Joined: Fri Jun 20, 2003 1:00 am
Location: so cal

Re: XF20 or OD18 Mods

Post by sds »

Plus it looks like a pontoon barge with a couple of alien pods strapped on the bottom.

Vs. TX18 and FX20, which are handsome boats.

User avatar
Randy
Active Poster
Active Poster
Posts: 218
Joined: Sat Feb 22, 2003 1:00 am
Location: San Antonio

Re: XF20 or OD18 Mods

Post by Randy »

I think the question is a simple one.

Like the XF20 is basically an enlarged GF18, Can we get a design that is an enlarged OD18, 21 feet long, 8'2" to 8'6" beam and maybe a tunnel option. Like the XF20, a low freeboard and still have lower HP requirements than production boats.

Examples:
http://www.flatlanderboats.com/Flat24.htm

Clinkster

Re: XF20 or OD18 Mods

Post by Clinkster »

Regarding the statement that there is not enough lifting area in the stern of the OD 18 for a tunnel, what if the hull is 20 or 21 feet? I think Randy captured it pretty well with his inquiry and the Flatlander is a perfect example of what is needed. As information, along the Texas Coast, a lot of the fishing is done while wading. So, yes we need to run across long stretches of open water, that can be rough, and when we get to the fishing area, which is generally shallow, we jump out of the boat. We are not always polling and throwing flies out of the boat like the Florida fishermen. It's just a different way of doing it down here. Any more thoughts on a modification?

Prarie Dog
* Bateau Builder *
* Bateau Builder *
Posts: 2330
Joined: Tue Mar 23, 2010 2:52 pm
Location: Penrose, CO

Re: XF20 or OD18 Mods

Post by Prarie Dog »

Randy, I've been looking at the various tunnel designs and a lot of the boats built on the Texas coast. Before high horsepower outboards were available there were and still are a lot of tunnel boats built for racing not for fishing. I think the function of the tunnel was to generate lift and reduce wetted surface, video of these boats blowing over is all over youtube. I think we can agree that doing that in a fishing boat would be hard on the occupants. I rode on a large Tran Cat about 5 years ago. It wouldn't go nearly as shallow as all the bs online would suggest and with a two hundred horse motor it would run about 35, it was smooth.
Moving forward to today I still look at the small Cat/Scooter boats and here are the numbers. Generally speaking they are from 18 to 15 feet long. The 18's use from 90 to 115 hp to run 30 to 35, if you look at pics of these boats the static draft is 8 to 12 inches. On the shorter boats in the 15' class, they are powered with motors from 50 to 90hp. Jaques says these boats are ineffective because the passage of the twin hulls disturbs the water in the middle therefore the motors have to be run down or deeper than even a flat bottom. Here are some interesting numbers that I have gathered over the last several months. The 15' cats with a 90 will run in the mid to high 30's and with a 50 will run in the high 20's. The 18's will run the lower speed range with a 90 and the high 30's and low 40's with a 115. A GF18 with a 50 will run 30. The GF18 is shallower and faster with the same horsepower. So it looks like the flat bottom is better in every way except ride quality than these scooter boats. We will soon know if the TX18 is a better compromise. :D

Randy, I know you're talking about boats over 20' so these shorter boats aren't the same. For comparison purposes I think you can reasonably extend the numbers to a larger boat except for one thing. Generally speaking boats gain significant weight for every foot of length over 20 ft.

Nate Hoyt
Frequent Poster
Frequent Poster
Posts: 12
Joined: Sun Apr 03, 2011 3:18 am
Location: DC

Re: XF20 or OD18 Mods

Post by Nate Hoyt »

Clinkster,

I had similar set of needs at one point. We hunted and fished the mouth of the Mississippi when I was in college. The perfect hull needed to survive hellacious wakes and nasty chop, yet still get you out of the marsh when the tide went out. I wanted to build a low sheer (i.e 15-17" cockpit depth) OD18. You could even go with a flush deck/flat sheer to reduce windage, but that would allow some water to come over the bow when you hit a big wake, so I wouldn't do it for my purposes. Such a rig would float shallow, yet get you home when the wind kicks up inshore. It is also a stupid simple mod of an existing plan. You could extend it 10% to get a 19.8' boat. You'd sacrifice a lot of offshore seaworthiness by lowering the sheer, but you'd be able to take 4' wind chop and the occasional 8' crew boat wake (I'd definitely make it self-baling). Add a jackplate, tabs and a cupped prop and you could run pretty shallow, although you'd have to slow down in the rough stuff to avoid blowing out. I haven't built it yet, but it is still high on the list of possibilities.

The PH18+10% or even the PH22 sound like they would work well also. probably better. I just happen to like dories myself.

Many hulls are drawn up by good `ol boys in their shops based on what they think sounds cool or what they already know. Hydrodynamics may or may not be considered. I can say this because I am a redneck who is currently building such a hull. The public will pay extra for a tunnel, so some hulls end up with tunnels when they shouldn't. If someone who knows hydrodynamics is honest and says he won't make it because it is a bad design, it is best to listen.

Boat fads come and go. If you hang a 250 HP motor on the end and add some sparkly gel coat, Texans will buy most of them...
:lol:

Nate

User avatar
Cracker Larry
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 22491
Joined: Fri Mar 11, 2005 3:39 pm
Location: Savannah, GA

Re: XF20 or OD18 Mods

Post by Cracker Larry »

Many hulls are drawn up by good `ol boys in their shops based on what they think sounds cool or what they already know. Hydrodynamics may or may not be considered. I can say this because I am a redneck who is currently building such a hull. The public will pay extra for a tunnel, so some hulls end up with tunnels when they shouldn't. If someone who knows hydrodynamics is honest and says he won't make it because it is a bad design, it is best to listen.

Boat fads come and go. If you hang a 250 HP motor on the end and add some sparkly gel coat, Texans will buy most of them...
You are a smart man Nate 8)
Completed GF12 X 2, GF16, OD18, FS18, GF5, GF18, CL6
"Ships are the nearest things to dreams that hands have ever made." -Robert N. Rose

Prarie Dog
* Bateau Builder *
* Bateau Builder *
Posts: 2330
Joined: Tue Mar 23, 2010 2:52 pm
Location: Penrose, CO

Re: XF20 or OD18 Mods

Post by Prarie Dog »

I know it looks like I have flipped on this topic. Fact is I have. I was explaining to Larry the other night that I try to keep my finger on the pulse of the fishing scene in Texas. To do this I watch a couple of websites down there and since fishing is the reason boats are often discussed. The trouble with reading endless BS is you often loose track of the facts and prior knowledge you had and forgot or ditched in favor of some new-fangled BS. That happened to me. I had already asked many of these same questions, read some of the same facts and been made aware of the struggles the tunnel boat builder Jaques tried to help. I forgot this info. Nate is right on the nut, shiny gelcoat and a 250hp motor will often sell a boat. When fishermen sit around knocking back sundowners, oftentimes the good boat is the fast one or the one with the biggest motor. The crazy part is good fuel mileage is often thrown in there with these other less than true facts. When these same guys repeat this stuff for ever it often takes on a halo of truthfulness it doesn't deserve. :doh: My apologies. Paul

Post Reply

Who is online

Users browsing this forum: No registered users and 9 guests