Build Instructions for the 4500BA – Assembly Part 1- Plates and Frames

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Finally, the time has come. Make sure you have those welding skills ready, don’t make this your first aluminium welding experience. Practice on some of the scrap that you get in the kit.

Lay those hull plates down edge to edge lining up the etched markings. Use some blocks of timber/ tyres or anything really to prop them up. As long as it’s the same on either side and will hold the plates steady. The blocks we used are about 130mm high. Meaning we get the desired angle at the aft, you could also try place a frame in to get the angle correct.


Note:- At CNC Marine most of our vessels use a variable deadrise. It starts at about 15 degrees at the transom but aggressively increases towards the bow. We’ve spent a lot of time and leading edge naval architecture software to come up with a hull that meets our requirements. This is to achieve a fine waterline entry but retain stability at rest and efficiency while on the move.

 Start at the aft end, and work your way forward putting a tack inside the fwd edge of one of the weld marks along the keel seam.

TIP:– When tacking up, put welds at the end of were you plan on finishing your final weld. That way you neatly cover the tack on your final run.

Go ahead and place that back frame in, in this case it’s called ‘F1’. Line it up with the etched markings shown on the hull plates.

NOTE:- The front edge of the frame lines up with the center of the etch or pen line marketed on the hull plates.

It’s generally good to put a tack on either side of where the stringer will go through. And then one close to the edge.

The cutouts vary depending on the kit, but most look like this. Stringers sit hard against the smaller face. There are extra cutouts blowing out the top and bottom. These cutouts make you able to get good access to weld the stringers to the frames.

Once you have completed the first three frames it’s time to insert the stringers. Making sure they are inserted curve up and slide easily through the cutouts in the frames. You can then go ahead and tack these every 200mm or so up until frame 3.


Note:- You can see in the previous picture that more than the first three frames had been put in by our boat builder. He had missed the part in the instructions to only put the first three frames in before inserting the stringers. This was not a problem but outlines the fact that it’s a good idea to pay close attention to the instructions.

The stringers align to markings on the bottom plate, these also show where you need to weld along the stringer. 

At the start you can put a tack at the end of these markings, and then when you go back and fully weld this tack should get covered.

It’s now time to start fitting the remaining frames. Start with frame 4 and pull together the hull as you go. You may have to use a pair of come-along’s at this stage to make it easier for you to pull the hull plates together.

Attach the transom. It sits slightly on top of the bottom plates. Here we have used a couple of offcuts tacked to hold it in place and give it a bit more support for the next couple of steps, at least until we have the sides tacked on.

Starting from the bow fit the chines, tacking every 100mm or where necessary to help pull the hull plates further into shape.


Tip:- In cases like this where the front of the chine is not quite lining up. We can employ a simple method to align the two. We grab an F-clamp and place it over the chine as in the below image. Close the clamp up lightly and then pull up on the end of it. This will cause a lever action and pulls the plate back in line. Use offcuts of timber to protect the ally.

We suggest using a bow lug cut from 100x10mm flat which we supply in each kit. In the kit you will find a template used to cut this out. Supplying this as a cut part wouldn’t work as we find it gets customised a lot and it is such a simple part for you to be able to make yourself.

CNC Marine gives you a measurement for positioning your bow lug, this is based on the ideal position for pulling your boat up onto a trailer. Though this can also be modified depending on the trailer setup that you go for. That is why we don’t provide a cut out in the bottom plates for positioning your bow lug.


Once you have figured out where you want your bow lug to go you will need to cut out a small slice between the bottom plates. Allowing you to fit your bow lug through. Once inserted through you are able to fully weld inside and out for support.

So, the bow lug is attached. Therfore it is time to fully weld the keel seam from the bow through to the third frame in, in regard to the 4500BA this is frame 5.


Tip:- Take your time to avoid putting too much heat into the bottom plates. Weld a section of about 15cm, then move and weld a spot at least a meter away. After the original section is cool, you can go back and continue this seam.

Welding this section of the seam takes you to cutting the stem bar. The stem bar should easily bend enough to be slotted through the cutouts at the keel seem. Tack this at intervals on each side and finish flush with the chine.


Note:- We provide an itemised cut list for all the parts that come as full length extrusions. Some people decide to go through and cut all these parts at the start, which means you have them all on hand when you need them. This is up to you.