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        Build Log Hedlund Class B Outboard Hydroplane

#1 Chinewalker Dec 28, 2009 03:21 PM

Hedlund Class B Outboard Hydroplane
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BOAT: A mid 1970s era Hedlund-copy B-25SS Hydroplane. 1:1 scale length is 9'6". Model's scale is yet to be determined. I am currently drawing the frames and shapes in 1:8 scale for 1/2A power, but may scale them up for an Aquacraft EP1 or Graupner GTX 650, if I can find one. The Hedlund was a popular stock outboard design back in the 1970s and incorporated an air entrapment bottom, often called the Hedlund Hump. My boat was a copy or "splash" of a Hedlund.

Nearly 10 years after I first hatched the idea, I am finally at a point where I can build my boat! I drew up some rough sketches for it back then, but didn't get very far as I ended up moving and lost my model shop. I now have a nice basement shop and I'm ready to begin! I spent a good hour over the weekend with the 1:1 boat, measuring, taking photos, etc. Spent some more time on the computer drawing up the frames, transom, cockpit coaming, etc. Still have a ways to go, but it's starting to take shape!

To get started, here are some photos of the 1:1 boat...

#2 Chinewalker Dec 29, 2009 11:27 AM

Frame Drawings
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I decided to move forward with the 1:8 scale version. I figure I can make my mistakes and tweak things in the smaller scale without committing as much in the way of materials. If it works alright in 1:8, I think I'll go on to the 1:4 scale for the EP1.

Here's what I've got so far...

#3 GILL RC Dec 29, 2009 03:56 PM

Got to love the neel-downs, fun to drive. Last one I had I had purchased an 8 footer for my step son. rebuilt it and painted it in Dallas Cowboy colors, with the blue stare on the nose. He then sank it in lake George with my buddies new 10 horse Johnson on it. I had floatation and it just tomstoned. Throw a line on the bow hook and pulled it back level dumping most of the water out. Buddy was not very happy.

#4 Chinewalker Dec 31, 2009 11:03 AM

Revisions made..
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Thanks John! I tweaked the frames and made a template for my cutouts. Hopefully I can start cutting and gluing this weekend! I ordered a Graupner GTX 650, which may eventually find its way onto a larger version of this.

#5 Chinewalker Jan 01, 2010 04:39 PM

Assembly begins...
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Got a good bit done today. Coamings and most of the framing put together. With a little imagination, it's starting to look like a boat! I used mahogany planking for visible areas and balsa for the frames and cross members.

#6 Chinewalker Jan 03, 2010 05:38 AM

Framing Done!
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Got a lot done Saturday morning...

The framing is pretty much done. I still need to add pieces for the sponson chines, but that's it. I even started skinning it last night, adding the rear chines with the "chicken wings". For the uninitiated, my 1:1 boat has a raised portion of the rear, starboard chine called a chicken wing. It was added after the boat was built to reduce the chance of digging the chine in a turn and flipping. Later versions had it as "standard" and many had them on both sides to maintain symmetry, although you'd never turn right hard enough to dig the port side chine.... I decided to go with symmetry on the model version.

I simplified the design in several areas. My original plan was go go for full frame and batten build, but decided to do more gluing and less cutting. Makes for a much quicker build.

I used solid balsa blocks for the bow area to give a bit more impact resistance over battens should we ever contact a dock head-on.

#7 MILLERTIME Jan 03, 2010 11:25 PM

Starting to look like a boat.

#8 Chinewalker Jan 04, 2010 10:43 AM

Bottom On!
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I got the bottom glued and clamped Sunday morning. Also did the battens and inside planking for the sponsons in the afternoon.

#9 Bob Bighinatti Jan 04, 2010 01:50 PM


YOUR going to need a bigger BOAT!!!
Bob Big:D:D

#10 Chinewalker Jan 04, 2010 02:09 PM

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Yeah, the single cylinder .049 looks much better on there ;)

#11 MILLERTIME Jan 04, 2010 11:45 PM

You have some nice old Outboard's.

#12 Chinewalker Jan 05, 2010 08:49 AM

Sponson chine planking...
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Back to the work week so shop time was short. I did get the sponsons faired in and glued the chine planking onto the sponsons. Hopefully I can get the sponson bottoms on this evening and then I can seal up the insides with West System epoxy.

A couple folks have asked about the butt joints I used for the cross members, etc. - I did that on this boat simply because it likely won't see much water time. I am doing this one more as a proof of concept hull just to make sure my lofting and drawing work went well enough to move onto the larger version. Strength, although important, was secondary to making sure I got the various alignments and curves right. At 14-inches long, it doesn't weigh much and the stresses if I do run it with a 1/2A outboard are minimal. The West System that I'm sealing it with will greatly strengthen what's there, too. On the larger version I will notch the cockpit coamings to run the frames chine to chine, and will also run the lateral battens full length on the sides and chines.

#13 GILL RC Jan 05, 2010 09:33 AM

Very nice. You are righ the stress will be light. he Atwwods are pretty smooth rinning I orefer the Sea Fury.
They aer on my site at www.jsgill.net I've been collecting the outboards for over 50 years.

#14 mxz70017 Jan 05, 2010 03:49 PM

Looking Good!!!
Hey Its starting to get It's look's now.Love getting some skins on an see how It look's!!!Alway's better then the bare frame look.Get some 3/4"an 1" as well as a 2" roll Of blue painter's tape.Sticks well to wood!!! Use It In cut piece's to hold things together.I use more tape now then I do clamps. It don't deform an crush balsa stick's either.

#15 Chinewalker Jan 06, 2010 10:37 AM

Bottom Sides DONE!
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Got a little more work done last night and this morning. The sponson skins are on and mostly shaped in! Still have a little fairing to do, but they're more or less finished!

MXZ, thanks for the painter's tape idea. I'll get a roll and try it out... It definitely would have made a few things easier...

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