XF20 Performance

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Prarie Dog
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Re: XF20 Performance

Post by Prarie Dog » Thu Mar 31, 2011 10:05 am

Semperfly
Reading your posts on this thread I have to wonder if you've been subverted by what I like to think of as the Texas Thing. It got me too. I lived there for 35 years and really doubted the performance numbers of these boats when I got here. What I mean is that skinny water boats in Texas that are purported to have all the wonderful characteristics of real shallow performance have huge motors on them. The boat designs on Bateau are real light and don't require as much motor as mold built fiberglass boats. Shoalwater boats in POC build a boat called the Flats 18 that is almost identical to the GF18 on here. I have a GF18 with a 50HP Tohatsu TLDI. It has almost identical performance to the Shoalwater boat with a 90. My GF weighs about 100lbs more than the Shoalwater's advertised hull weight ready to go. The basic hull is over 300lbs lighter than the Shoalwater. Check out David Sours DE25's performance with one 90HP Etec. If that boat had been built conventionally it would require two 90s to achieve the performance he gets with one motor. The point is, to get the benefit of these designs you have to think light, not more power. If you look at the performance numbers of the TX18 with a 60 and think about how big a boat it is I think you'll see what I'm talking about. :D

We'd love to have you come to the meet.

Edit 1. Sorry, David Sours boat has a 115 etec.



hooter
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Re: XF20 Performance

Post by hooter » Mon Aug 01, 2011 6:39 pm

After the Texas meet I am revisiting this performance idea and am perplexed...

If you look at a Majek Redfish line 20(which anybody who visited the Texas meet will recoginze it as there is one around every corner in POC) the dimentions are almost identical to the XF20. 20 feet by 8 foot beam roughly. Tunnel

The draft is a function of displacement which is determined by shape, weight, balance and volume. Everybody I've read seems to caution about putting too big a motor on the XF20 as it is "way too heavy". How is it that production manufacturers routinly put 150 HP motors on these boats and get speeds of 38-45 mph (and still run super skinny) but the fastest XF 20 I have seen is pushing 28 mph. I'm not a speed freak but am thinking put a little bigger motor and balance weight forward and go faster. why is this wrong?

I guess I am intrigued by DavidTX and his upgrade from a 60-90hp 4 stroke on the sled (and the resultant perma-smile). If you have a boat that is 8 feet wide and 20 feet long, what's another hundred pounds? 1/4" if properly balanced? why is this "way too heavy"? prove me wrong! :lol: Would the addition of sponsons adjacent to the motor help balance this increased motor weight by providing greater surface area and therefor bouyance (but thereby increasing weight and decrasing draft in the stern? )

I'm not a nautical engineer but I want everything in a build. Enough HP to "get it" but the skinniest draft possible. Just trying to figure out how the production boats do this but we can't seem to get the speeds they are generating.



all input appreciated.

hOOter

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Re: XF20 Performance

Post by Prarie Dog » Thu Aug 04, 2011 1:09 am

Hooter
I'm with you. When you read all the claims about the speed and shallow draft capabilities of some of the Texas Boats a guy gets real wowsered. There doesn't seem to be much doubt that the Majek RFL runs shallow and will go like hell in smooth water given enough horsepower. The stories about how rough these boats are in a chop are also consistent with an XF20. I think the RFL would probably track better than the XF because it is turned down at the chines which hurts the shallow draft thing. This is probably a compromise by the designer to build it to go faster than a flatbottomed boat without loosing control of it. There are also some constants that no designer can get away from. It takes close to 8 gallons of fuel an hour to make 100 horsepower. As the engines on these boats get more powerful, the fuel load gets larger to keep the range constant. It is a kind of a trap, bigger motor=bigger fuel load=more expense=deeper draft etc. etc.. The XF20 is a no holds barred attempt at the skinniest shallow water boat possible. If a guy could solve the tracking problem and figure out how to make the tunnel more effecient he might be able to do what you're shooting for. Running back in time I think about a lot of 18' tunnel boats built in the 60's and 70's that would run in the 60 and 70 mph range with one 100hp Merc. on them. It's kinda funny that 50 years later they're having to put 300hp on a 20' cat fishing boat to get similar performance. Makes me wonder if were moving forward or if they're hung in some kind of a style trap they copy to sell boats, kinda like monstor mudders on the go to town truck. :lol:

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Re: XF20 Performance

Post by jorgepease » Sat Feb 11, 2012 12:36 pm

hooter wrote: I guess I am intrigued by DavidTX and his upgrade from a 60-90hp 4 stroke on the sled (and the resultant perma-smile). If you have a boat that is 8 feet wide and 20 feet long, what's another hundred pounds? 1/4" if properly balanced? why is this "way too heavy"? prove me wrong! :lol: Would the addition of sponsons adjacent to the motor help balance this increased motor weight by providing greater surface area and therefor bouyance (but thereby increasing weight and decrasing draft in the stern? )

I'm not a nautical engineer but I want everything in a build. Enough HP to "get it" but the skinniest draft possible. Just trying to figure out how the production boats do this but we can't seem to get the speeds they are generating.

all input appreciated.

hOOter
I just ordered my plans for this boat. I agree with your reasoning. One of the mods I am planing will be to do away with the tunnel and use a jet ski propulsion system to power the boat. Weight is about 100 lbs more than a standard outboard 90HP but the jets are rated from 150 - 300 HP. Im sure its going to alter CG but I will wait to add console live wells, gas tanks till I see how its affected.

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Re: XF20 Performance

Post by gstanfield » Sat Feb 11, 2012 1:13 pm

If you look at a Majek Redfish line 20(which anybody who visited the Texas meet will recoginze it as there is one around every corner in POC) the dimentions are almost identical to the XF20. 20 feet by 8 foot beam roughly. Tunnel

The draft is a function of displacement which is determined by shape, weight, balance and volume. Everybody I've read seems to caution about putting too big a motor on the XF20 as it is "way too heavy". How is it that production manufacturers routinly put 150 HP motors on these boats and get speeds of 38-45 mph (and still run super skinny) but the fastest XF 20 I have seen is pushing 28 mph. I'm not a speed freak but am thinking put a little bigger motor and balance weight forward and go faster. why is this wrong?
I think one of the issues at hand is that these boats are designed to be light. I looked at that Majek and it has a hull weight of 1100 lbs as compared to the hull weight of a XF20 which will come in about half that. The XF can be beefed up to take the extra power, but then you're adding weight which adds draft, etc etc.

The Majek has a static draft of 8" while a XF20 will draft about 2-3"

It's all in what you want out of a boat. :wink:

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Cracker Larry
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Re: XF20 Performance

Post by Cracker Larry » Sat Feb 11, 2012 1:32 pm

The Majek has a static draft of 8" while a XF20 will draft about 2-3"
Seth's XF20 wasn't drawing more than 8" when we put 19 adults on it, and we had the scupper drains pulled :!:
Completed GF12 X 2, GF16, OD18, FS18, GF5, GF18, CL6
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Re: XF20 Performance

Post by jacquesmm » Mon Feb 13, 2012 9:21 am

Those production boats may run shallow (not as shallow as the XF20) but their static draft is much more than the XF20 plus, they have a very bad trim by the stern.
Static draft counts, you will not float in less than 12" with those boats and you can't take off from shallow spots.
Whatever they say in the brochure, if you have the same waterplane (beam by length) and trim, you will have more draft if the boat is heavier.
All the advertising tricks can't beat the laws of physics. :wink:
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Tex 2009
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Re: XF20 Performance

Post by Tex 2009 » Mon Feb 13, 2012 11:46 am

I fish LLM along with the Galveston Bays and the water you sometimes need to get in is super shallow. The production boats may run shallow, as mine does, but come to a stop in these shallow waters and you are beached, I know from experience.
The xf is designed to be a shallow static hull, look at the pics of the designed hull as is, you can see the drain plugs above water level.
My boss has a shallow sport, which this hull cant be beat for shallow water production hulls, and he and I have pushed it off mud in the South Bay.
Semper, Tails is building a xf hull right now in Port Isabell. You can find him in the builder forum. Get with him and take a look at his hull.
Just my 2 cents from experiences in the shallow waters.
Doug Grall
Huntsville, Texas

jorgepease
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Re: XF20 Performance

Post by jorgepease » Mon Feb 13, 2012 1:01 pm

Those production boats may have other redeeming qualities, it seems there is always a tradeoff. Smooth ride, speed, dryness etc

My XF plans are on the way. The static draft appeals to me for fishing and exploring but I also need to get up on plane and get where I need to be (30-35 mph is plenty fast for me).

My Carolina Skiff (17DLX) is solid and dry but she pounds a bit at times and I expect even though much shorter, she probably handles the chop better than the XF 20 because of the hull weight. Im hoping the xf, beefed up a bit will handle it at least as well. At that point though, I may be drafting as much as the skiff .. so .. in the end I am building an xf because I want it just the way I want it and for the enjoyment of doing it.

I wish people would post some videos of them running their boats in different conditions ... like all the other boat mfg's have.

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tobolamr
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Re: XF20 Performance

Post by tobolamr » Mon Feb 13, 2012 4:02 pm

viewtopic.php?f=2&t=20040&hilit=xf20+marker

'nuff said! :lol:

Oh, and can anyone find the thread about the Phantom series boat that had a log core the hull, and they ran back up-stream a few miles to land it? And didn't sink? Jacques KNOWS how to build boats!

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