Raised sole on xf20

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wwsmith
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Re: Raised sole on xf20

Post by wwsmith »

Personally, I agree with the self-bailing idea. Very nice to wash the deck down a could times a day and have it easily flow out the back. I'd suggest making the drains fairly large. My current boat and previous boat both had 1 1/4" holes for drain tubes. They would work better if they were larger. Most that I see now have larger openings and they work much better.

fallguy1000
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Re: Raised sole on xf20

Post by fallguy1000 »

Matthew Anderson wrote: Mon Feb 15, 2021 1:09 am Ok so here are my calculations, please feel free to interject any thoughts.

The plans give a completed hull weight of 810#. I will be adding two additional stringers. Floatation foam in the entire sole. All surfaces will be glassed. My D15, Forever Young, came in 20% heavier than the plans predicted, this was due to it being my first build, excessive epoxy and fillets in places, lots of fairing, etc... so let’s say the hull will end up @............................................975#
Yamaha 4st 70hp....................253#
Jack plate..................................33#
Batteries..................................150#
Fuel 20 gal & tank...................135#
Live well 30 gal.......................250#
Ice and chest............................50#
Passengers.............................500#
Controls and rigging..................50#
Gear..........................................30#
Trolling motor............................80#

Grand total............................2506# This would be Tournament type weight, by no means everyday fishing weight.

Draft at DWL = 2-1/2”
Displacement at DWL = 865#
PPI = 412#
Extra weight above displacement at DWL 2506# - 865# = 1641#
1641# / 412 # per inch = 3.98” (4”)
4” + 2.5” = 6.5” of draft at full weight.

If I raise the sole to 6.5” the boat would be self bailing under this much load?

Have I figured this correctly or am I missing something?
Where does the skeg end up at 6.5"?

Is it like 12" deeper or 18.5", or do skinny water guys run prop jist touchin so skeg is 12" deep?

I am jist curious.

Personally, if I were building a flats boat; I'd be pushing for drafts less than skeg depth or tunnels for some water. All a bit above my paygrade, but looking at moving to Corpus Christi and see all that skinny water on my navionics.
My boat build is here -------->

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wwsmith
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Re: Raised sole on xf20

Post by wwsmith »

I measured quite a few tunnels before starting a modified XF22. The major complaint about them is how much the hurt speed and fuel economy. After looking into the more popular brands in our area, I found many tunnels are about 9" tall. You can imagine how much drag that must create. Also, these tunnels are not raked. They start at nothing and increase to full height at the rear. I was interested in JM's design with the raked tunnel in hopes that it would have the same effect as the taller tunnels (using the hump that is created) without such a huge tunnel to drag it down. Will have to wait a few more months to see if there is an advantage. My goal (and the goal of the others, I assume) is to have the option to get the prop above the bottom of the boat. I've seen quite a few successful cases using low water pickups.

Hopefully others will share more info. It's a topic I spent too much time thinking about in the early planning stages, and I'm still not sure I have it figured out. :doh:

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Re: Raised sole on xf20

Post by jacquesmm »

wwsmith wrote: Wed Feb 24, 2021 8:56 am . . . Will have to wait a few more months to see if there is an advantage.
I designed that tunnel more than 20 years and it has been used in hundreds of boats. Waiting a couple more months will not change anything.
I also designed bad tunnels. I did not put my name on it. I remember a particular production boat which was good all around but the CEO (it was a big company) insisted on the deep taper you describe. I refused to draw it but he had the tunnel designed by another engineer and grafted it to my hull. The result was really bad.
My reversed taper tunnel works well when the boat is built as designed: no added strakes or skegs.
I got the idea from a design by Uffa Fox.

There will always be a price to pay in performance. A tunnel will always disturb the proper flow of the water but some shapes have less detrimental effect than others. Details matter too and they are on the plans: the forward part of the tunnel, where the water enters, must have rounded corners but the exit edges must be very sharp.
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Re: Raised sole on xf20

Post by jacquesmm »

For the sole, your math is right and good enough for the purpose. As designed, the sole is at 4.5" draft. Raise it by 2" to 6.5" and it will fit your planned displacement.

Now, why worry about self bailing? When I started sailing, I routinely went offshore on boats that did not have a self bailing cockpit. Everybody did, it was considered normal and safe. The XF20 is designed for inshore use. Cockpit drains can be plugged and if you want absolute safety, the boat can be built with positive buoyancy using 2 part foam.

Just my preference, it's not complicated to raise the sole if you prefer that.
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wwsmith
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Re: Raised sole on xf20

Post by wwsmith »

My tunnel is built to plan. Only waiting a couple months for the rest of the boat to be finished! Now that I think about it, it'll likely be longer than that, but we're getting there.

I like self-bailing for cleaning fish blood and slime. :D Nice to rinse off with a bucket of water every now and then.
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TomW1
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Re: Raised sole on xf20

Post by TomW1 »

Fallguy I assume you are questioning the skeg on the motor since there are only small skegs on the very outside away from tunnel on the bottom of the XF20 if any. It basically remains the same as it is now on the 20" transom with the jackplate. Depending on the motor skeg protecting the prop 6-8-10" below the bottom of the boat when starting up and when raising the motor to get the affect of the tunnel about even with the bottom of the boat . So that would add an additional 4" from the original specs. Hope this makes sense.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

cape_fisherman
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Re: Raised sole on xf20

Post by cape_fisherman »

wwsmith wrote: Wed Feb 24, 2021 2:26 pmI like self-bailing for cleaning fish blood and slime. :D Nice to rinse off with a bucket of water every now and then.
Sometimes non-fishermen don't grasp the importance/convenience of some features.

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Re: Raised sole on xf20

Post by TomW1 »

cape_fisherman wrote: Wed Feb 24, 2021 8:36 pm
wwsmith wrote: Wed Feb 24, 2021 2:26 pmI like self-bailing for cleaning fish blood and slime. :D Nice to rinse off with a bucket of water every now and then.
Sometimes non-fishermen don't grasp the importance/convenience of some features.
Yepper!
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Matthew Anderson
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Re: Raised sole on xf20

Post by Matthew Anderson »

Pete, thank you for taking the time to show me your boat. Great build! I know I’ve picked the right hull for what I’m looking for in a fishing boat here in the upper and lower Laguna Madre.

We mainly wade fish so a lot of getting in and out of the boat. Lots of mud and fish slim on the deck. Raw water wash down is a nice luxury on a flats boat here. Most of the time I run in 16” to 36” of water. Lifting the motor and drifting, poling or even walking the boat in 7 to 8” will happen often. Being able to get up on plane in 12” to 14” is the goal.

Pete your boat rode higher in the water than I anticipated, however we were running pretty light.

Questions for Jacques: can flotation foam lower the water line. My understanding of volume of displacement water weight equals buoyancy. The weight of the foam is more than air so shouldn’t the displacement with the foam be more than without. I understand the benefits of the foam being in emergency floatation, quietness within the sole which is why I intend on using it under the entire sole.

You also mentioned the sole of the xf20 is designed at 4 1/2”, is this an average along the sole? At mold “D” I measure the sole to be 5 3/4” given the stringer, bottom panel and deck thicknesses. 2” seems like a lot to raise this sole by, but again being able to wash down the deck on the water at the weight I described is important to me.

Thank you everyone
image.jpg
Now is the time to determine stringer heights.

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