Build Instructions for the 4500BA – Assembly Part 2 – Sides and Gunwales

CNC Marine we are here to help

Find your aft stringer brackets, they are the small triangle guys, generally with a curve on the top.

Note:- You may notice that we try and put curves instead of straight angles where we can. Adding a curve into something like the aft stringer brackets significantly reduces cracking caused by stresses acting on a single point. The curve acts to dissipate those stresses over a larger area.

These brackets are different sizes, so careful here. The idea though is that once aligned on each stringer you should be able to put a straight edge over the top of them to connect them all.

 

Finally, the hull Sides, this is the part where you really start to see a boat appearing.

Note:- two people required for this task. More on bigger boats. The side sheets are always made from a single piece, so no ugly butt welds up the side of your boat. This means they are heavy, try holding them up yourself let alone hold them up from one end and welding at the same time.

Invite a mate over because you need an apprentice for this one. Start by finding the correct hull side plate, the etched lines need to be on the inside.

Once you have tacked on both side plates you are in a good position to weld the foredeck on, you may need to use a strap or come-alongs to pull the sides together at the bow so that you can line this up.

When the foredeck is tacked in place you now have a good position to start attaching your gunwales. Using the aft edge of your foredeck and the edge of your side sheet to locate. Tack, and then move aft tacking as you go, bringing the top of the side sheet into line. Stitch weld underneath gunwales but leave the top edges for when you’re adding your fender. Then do the same with the gunwale sides.

Note:- To avoid show through the frames do not meet the side plates. When building this can seem like a mistake, but you haven’t done anything wrong there is a 10mm gap.

 

Start at the bow, align the forward most corner inside edge of side plate to top edge of chine plate. Put a tack. Then get your apprentice to work his way back, as you do, using the length of the side plate to lever it into position. Put another tack 5cm along from the first one and continue right the way aft.

The sides should line up everywhere, which is the beauty of using very powerful software, loads of experience, and finally, CNC cut parts. As with the gunwale and chine though the plates should run past the transom plate slightly. Allowing for a good fillet weld on the outside.

 

Tip:- Take a step and really have a look at what you have achieved so far, you can finally start seeing your boat take shape. Walk around, get on one knee and look at the curves and angles, make sure the frames are all level, and that your happy with how everything is sitting.

Time to fit the transom stiffeners, we do show cut lengths for all these but there are some things you need to think about. What is your leg length of your engine for instance? With the 4500BA we cut the transom to suit a 25inch leg length, we also etch a line which is to suit a 20inch leg length. It’s time to decide, so speak with your engine dealer.

Note:- Many of our designs have fixed leg length, this information should be on the General Arrangement that you receive right at the start of the journey. If you’ve already got your engine then you need to make sure that either the design already matches your leg length, or that we know about it and we modify the design to suit your leg length. (please be aware that modifications can come with extra costs)

Tip:- When welding on the transom stiffeners the transom plate can buckle and move all over the place. To minimise this, use lengths of flat bar tacked to the outside of the transom to keep the transom straight.

At this stage it’s a good idea to attach your brace/s. It is important that you stick to the correct measurements for where the brace is to be placed, and make sure that it is equal distance from the transom at either side. This allows you to check square of the vessel.

Tip:- We provide extra flat bar in each kit for extra bracing, putting a bit of flat bar on the provided brace is a good idea to stiffen it up further.

Generally, at this stage your sides will be sitting slightly wider, so you may need to get a ratchet strap and pull the whole boat in until you can fit your brace on. Now throw a tack on to keep the brace in place.

Note:- The brace across the midships gunwales remains on until you have done all the major welding. Otherwise there would be too much movement with the amount of heat you’re putting into the sheets. Also be mindful that the brace will be removed, depending on how your planning on finishing your gunwales you might want to be mindful of the marks your putting into it.

A welding diagram is part of every drawing set, now is the time to have another good look at that. Using the weld diagram fully weld the stringers and frames to the bottom plate, stringers to frames, chine/bottom, chine/side and keel seems.

Tip:- Once again let’s re-iterate that you really need to avoid heat distortion. You need to move around and not weld big sections in the one place. This will put too much heat into the plates which will be to the detriment of the final product.

After all that welding there’s a couple of small items that can be done. The first one is the foredeck surround. This is one of those areas that can be fairly customised. Here we stuck with the standard of bending up some 40x5FL to go around the anchor locker. There is a lot you can do here so have a plan of what your final anchor arrangement will be and start to execute at this stage.

Note:- One of the beautiful things about building your own plate boat is the option to highly customise the build. You get to make decisions about each and every bit of the build. It’s your boat, that you’ve built, we’re sure you’ll put a lot of yourself into it.

Depending on how you’ve setup your new boat you may need install a plug below the deck line. You can easily buy these off the shelf. You need to drill a hole in the lowest part of the transom and insert the aluminium outer. With this it’s easy enough to completely weld and seal it up.

Finally, it’s come time to turn your boat over. Often the hardest thing you’ll do with your new build. Space is an issue and having enough strength to pull it over. In regard to the 4500BA and other smaller models. Getting a couple of mates together to lift up and roll over is a very easy task. As long as you have the space on the other side that is. If you don’t think you have enough space, there are ways around it.

Note:- On a lot of our builds we specify the use of turn over lugs to assist with this step. In regards to the 4500BA welding lugs onto frame 2 and frame 4 is suggested. Then we also give a weight at current stage(180kg for the 4500BA).

Tip:- Drag a build out of your single garage or like space out to the road or yard and turn it over there. Then drag it back. You could build a simple trolley to drag out, or even just some coppers logs.

Fairly straight forward what comes next. Weld all the seams. And make this thing water tight!

The keel on this boat is cut from 50×25 channel, cut 150mm triangles out of the sides on each end and then bend the top down. Weld up seams and before you know it, it’s time to roll her back over.

The underside now with fully welded seams it’s time to go right through and do a bit of a tidy up of anything you think you may have missed from the previous steps.

You’re not going to see anything dodgy here but when you’re in your shed welding on a Friday night with a few beers in you. Well you may have missed something.