ML Boatworks PX335 build/ instructions. For use with the PX300, QX400 O/B Tunnels

Well, I have had a lot of interest in the PX 300(FE) and NX 300 (Nitro) 30" o/b tunnel frame up kits. A lot of people have asked for guidance with the build, so last weekend I spent about 7-8 hours from start to finish, and put together a PX335 kit. I am actually wishing I had done these frame up tunnel kits a LONG time ago. The build went flawless, and is very very symmetrical from left to right sponson. Hot wiring foam on the old wood over foam hulls was a real nightmare to get correct, and this took all the hard work out. Instead of 3-4 days of wait time with the wood over foam sponsons, I can have everything but the sponson top decks done in as little as an hour per sponson! Also, what I found to be nice, is this 33.5" PX335 FE hull, without gear or cowling weights only 3 lbs exactly on the scale...that is only around 8 ounces more than the ps295 foam hull weighted...so that is very acceptable as far as weight is concerned. Along with a gas tunnel I am working on, I will be building the PX300, NX300, and QX400 tunnels in the coming couple of weeks, and sharing info on those as well. Once the PX335, and QX400 are tested, I will move forward with an NX320, which will be a 32" hull for mod B tunnel, and an NX400, 39.5" hull for mod 7.5, and an NX350, 35" hull for stock 7.5. I will also take this info, compile it and have a pdf instruction manual soon. As always, I enjoy sharing these builds with everyone as they are fun! This hull will be powered by a Neu 1521 1.5d 1850kv motor, OS lower unit, and castle ice esc. Anyways, I have a LOT of pics, so bear with me uploading all of these. I will be working on that over the next couple of hours, so hang tight, and ask questions maybe once everything is up, or if you would like to see something specific, please just PM me and I will do so! Thanks, Mike

First, here is a few pics of most of the kits vital parts:

Sponson framework:



Sponson sheeting:



Center section upper and lower pans, forward to aft members, radio box sides, and internal framing:

The first thing I will suggest, is a tool Phil Thomas told me about a few years ago, a Stanley Sur-form. If you don't have one of these $7 tools..GET ONE, it has changed my boat building life! It is by far the easiest way to avoid breaking through layers of plywood while trying to sand 90 degree surfaces flush.



First thing you will want to do, is grab sponson crossmembers #1L (there will be a frame with holes, and one with out) and #1R (same as left side, one with holes, one without), and glue them together. This makes up the sponson transom plates:



Now find your sponson Keelsons (the long inside edge of the sponsons), lay them on your flat board, clamp them down, then start dry fitting your sponson internal framing (All framing has numbers, and an R for right, and an L for left that match with number on the sponson keelson plates), and then put the sponson outside edge (sponson shear) in place like this:



As you can see, that outside sponson shear will lot into the crossmembers, forcing the parts to be 90 degrees to the keelson..Its almost fool proof!



Now glue the nosing, one above, and one below the sponson shear at the front of the sponson:

Once you have dry fitted the above parts, you can CA them in place. Using a 90degree angle is a plus as you can push it against the transom area of the sponson, confirming it is square. Once you have that done, you can then glue in a 1/8" x 1/8" basswood stick like shown below.



Once that basswood stick is glued, sand that outside face in preparation for gluing the outside edge sponson sheeting. And glue like below:



Now glue in the non trip 1/8" x 1/8" basswood support stick:



Now glue the ride pad support 1/8" x 1/8" basswood stick:

Now you can use your Stanley sur form for the first time, and flush in the lower edge of the outside sheeting like so:



And finish sand with a sanding block and 180 grit to smooth it:



Next, glue on your sponson non trip sheeting. The pictures below show it already sanded in flush, you will have overhang on each side...once glued, go ahead and use your stanley sur form and flush in each edge.







Now, I suggest getting something to elevate your sponson from the building board, as you are going to want the inside ride pad edge to overhang so you can sand it properly after installed. I used (2) 3/16"x 3/16" basswood, layed them on my building board, then clamped the assembly down:

Now, find your ride pads, and dry fit them, and what you want to look for is excessive overhang on either side. On the outside edge, it is critical to sand improper overhang before gluing. This outside edge stay blunt, and if you install it without checking for a nice clean blunt edge that runs parrallel to the non trip surface, you may have some areas you cannot sand clean later. I just marked my ride pad where I felt it needed sanding down, and sanded it on a disc sander. :



Your ride pad outside edge should resemble this after gluing. You will notice the inside edge has a lot of over hang, and the outside edge is very clean and tight against the non trip all the way forward:



Once you have the ride pad glued, now remove the clamps, and sand the inside edge with the sur form like this:



Now, Mark on your ride pad from the inside edge, outward, 1-3/8" in two locations. One at the sponson transom, and one around 10" forward. This will ensure your secondary ride pad is parallel to the primary pad that is already installed:



You can see where I am pointing to the dot that is around 10" forward:

Once the primary pad is marked, you can now dry fit your secondary ride pad:





Here you see the overlap of the secondary pad on the inside edge.. I suggest removing some of that...leave some overhang, but removing some with a saw now, will make your sur form sanding shorter once the secondary pad is glued in place:



You can see I marked leaving make 1/8" overhang:



Now you can see where I marked a line all the way forward so I had a guide while sawing:

Now that you are done with the dry fitting, reclamp your sponson to the flat board, with the elevated platform so you can glue your secondary pad:



Add some CA, and line up the secondary pad with the dots you put on your primary ride pad earlier, and bond:





Now sand away that overhang of the secondary pad:

And your finished ride surface should look like this. Repeat all the above sponson steps with your other sponson. We will glue the sponson top deck later.



Its a good idea to store the sponson clamped together until you are ready to epoxy the interior...like this:



OK, so lets move to the center section. Gather all the center section parts, and lay them out. The pics in the 2nd post should have familiarized you with the parts. We will start by dry fitting a few things:



Once you are get a feeling for how the crossmembers fit, it is time to laminate a few parts. The transom plates A1, A2, A3, and A4 will be bonded together first:



There are also two plates labeled "H" that make the forward nose of the center section...glue them together too:



Then you will have a double layered radio box/ center frame. Bond like the following for each side:

Another shot of the center frames...note, only one side is bonded in this pic:



Now, dry fit the transom plates, frame B, frame G, and the radio box sides..once dry fit, insert the assembly into the floor pan toy tabs, only checking for fitment at this time:



At this time, tape the front area of the radio box, just to keep it secure, and it is now time to bond plate "H" to the floor pan like this:



While your dry fitted assembly is still loose, insert a 1/8" x 1/8" basswood stick in the location I am pointing too:



I now suggest clamping your pan down so that it is good and flat agains the flat board. Keeping the floor pan flat, without a twist will be key to your build. If the center is twisted, the sponsons will not lay flat on the board later on!

You can now start inserting the other crossmembers:

It is now time to slowly glue all the crossmembers, and radio box plates down, being sure all is square. Once you have those bonded, you can start putting in the radio box lid parts. Having them installed will help minimize twisting of the assembly, making the rest of the center section build a little easier.





The lid and tab. If you haven't noticed by now, there were two tabs in the kit. One for the hatch, one to support the rear area where the hatch lays down on.



I also ran some 1/8" x 1/8" basswood sticks down each side of the radio box for extra strength:



and tape it shut for now, and add the upper piece of 1/8" x 1/8" basswood stick:

Now add this piece of 1/8" x 1/8" basswood:



And add the outer side plates, and remaining 1/8" x 1/8" basswood stick. Please note, the kit offered will not have all the crossmembers protruding through the outside side plate...this was an error on my part!

Now test fit your sponsons to center section toy tabing. It should lock right in!



On the final kit, I have gone back and added 1/8" x 1/8" slots in the center of the top of the crossmembers so a basswood stick can run forward to aft. I added this to my kit as it helps keep the sponson from twisting.



Now we are to the epoxy stage for the sponsons. My first suggestion, is to put masking tape on the inside sponson plate (keelson), this will help keep epoxy from leaking through and bonding your sponsons to your building board! You can also cut up some fiberglass cloth or carbon fiber and lay it in your ride surface area before epoxying.



I also suggest adding some floatation to the inside of the sponsons, and center section. Here is what I used:





Once you have coated the inside of your sponsons with epoxy, and pushed the foam floatation into place, I highly recommend clamping you sponson back on the flat board.

Now that your sponsons are drying, its a good time to finish up the final sanding on the center section framing where the center top deck will bond...this means its time to use a sander to bevel the front nose so the deck will lay down:



Then, take some scrap 1/8" basswood stick, and cut it up, and add it to the crossmembers at the top. This will increase your bonding strength when epoxying the top deck down:





Now cut some foam for your center section floatation:

Now, add some masking tape to the bottom, covering the toy tab slots..to remove the chance of epoxy bonding your center section to the building board!



Its also time to trim the foam around the dowel rods (you can either add, or dont add the dowel rods, they are your choice. 5/16" dowel or brass tubing is required). After you are happy with your dowel and foam, remove them, epoxy the inside, and replace..you will end up with this:



While the center section interior epoxy is still wet, its time to epoxy the bottom side of the top deck, and tape it down on the center section framework. I also like to use CA around where the top deck touches the radio box. Its hard to get tape to hold that area properly..a touch of CA in that area will ensure your deck stays in place while drying. Remember to clamp and weigh down your center section corners, and middle..remember, keep it from being twisted as once the top deck drys you cannot remove any twist!

Now do a dry fit clamping of the sponsons and center section once the parts are dryed. Just look over the bond seam between the 3 parts and make sure its nice and clean, and take a 90 degree angle and check the tunnel to sponson fitment..should be good and square..if not, your center section top deck may be pushing the sponson out of place...check it over:



another view



While dryfitted, check and make sure your sponson inside edges are nice and flush to the building board. If not, look check for twist in your center section, or if your ride pad is not sanded properly.



Make sure its 90 degrees and square!



While clamped you should go ahead and bond the stumble pad to the bottom of the center section...DO NOT bond the stumble pad to the sponson yet..just have it pushed up against it. You will be gluing that surface when you permanantly bond the sponsons to the center section later.



The trailing edge of the stumble pad will need to be around 17.25" forward of the sponson transom. This applies only to the PX335..... The PX300 and NX300 is 16.2". The QX400 will be determined soon.

See how the stumble pads stay bonded to the center section, but not the sponson at this time:



Now its time to bond the sponson top decks: This is the most critical part of the build besides the center section top deck. If you have a twist in the sponson after the top deck is on..the twist stays!



In preparation for the top deck bonding, you will again want to put down a riser on the flat board. This will allow you to clamp down your sponsons while the top deck sheeting drys, ensuring the sponsons do not get twist while you tape the decks on!



Epoxy the decks on, tape them to the sponsons, and put them on the riser, and gently clamp in areas that do not affect the top deck.



Once the sponson decks are dry, using your sur form, and sanding block and clean up all the outside edges:

add epoxy on the bonding area between the center section, clamp the 3 parts, double check with your 90degree angle to be sure the sponsons to tunnel are at 90 degrees, make sure your ride surfaces lay nice and flat on the building board..from the sponson transom, to around 11" or so forward. If you have more than maybe 1/32" gap, I would really look over your kit and see what is causing that before doing the final bonding of the 3 parts.

Here is the hull after clamps removed (I used the same clamping technique as you saw a few posts above while dry fitting the 3 parts):



And finally bond your air brakes:



Another shot of the finished product. Now you will need to bead seal with epoxy and silica all the way around the bonding area of the sponsons to the center section. Once that has dryed slightly, you can brush the rest of the hull with epoxy sealing coats. I will have pics of that this week when I add the bead seal and epoxy. So far, only 7-8 hours have been spent on this build..not to bad! Keep an eye on the thread. For now, this is all!

Woke up early and worked on seam sealing the critical areas. You can see from the pics were I taped off so the West systems mixed with Silica would be easier to focus in the corners. This step is worth the tape and time as it makes for a much cleaner bead.









The thickened mixture of West Systems 105 w/ 205 hardener, and 406 Silica

You can kind of see the bead in the seams. When I get home today, I will scuff the bead (since I was not home around an hour after applying the silica mix) and apply the first coat of west systems 105/ 205 epoxy on the exterior. You can also see I did however epoxy the inside of the radio box