Lessons Learned While Enjoying Sea Sled Madness

[DogCavalry]

Our boat, Serenity, is not finished, but is on the water generating income, so maybe it's time I discussed the process from a more objective perspective.

 

[DogCavalry]

It took us three times as long as I thought. If I started again with a proper shop, I could get to this point in six months, but without plans to work from, most of my time was figuring out the next step.
So lesson 1: Work from plans if possible. If not, expect a huge increase in time, and consider the extra time spent as part of the fun.

 

[DogCavalry]

One of the most painful and frustrating things was glassing the hull. The biax we used would distort across the width of the roll at the drop of a hat, getting wider and shorter, and ruining the piece. Along the length of the roll it was stable. So we should have glassed the hull from port to starboard, not bow to stern. That would have helped immensely. And the hull is strip plank composite, so transverse strength was more important anyway.

 

[baeckmo]

....glad you phrased "while enjoying...." and not "suffering from....."; that's the positive attitude necessary for a boatbuilder!

 

[DogCavalry]

If I did it again, I'd still use strip plank composite construction. But I'd be more careful about my material source. We had uneven drying of wood after the hull was planked, so there was a lot of sanding and filling of gaps.

 

[gonzo]

If you start a thread called "My next project", we will come over with a straight jacket.
Congratulations on your perseverance!

 

[DogCavalry]

If you start a thread called "My next project", we will come over with a straight jacket.
Congratulations on your perseverance!

Lol! Thanks @gonzo . But I suggest you come over with an appetite, and an overnight bag. Lots of food in the fridge, and guest bedroom waiting if you drink too much Canadian beer.

 

[Ad Hoc]

... but without plans to work from, most of my time was figuring out the next step...

This is one of the most common mistakes made by amateurs.
Because linked to that is - the design!

There is the inevitable excitement and thrill of building you're own boat, and the thoughts get all misty eyed and viewing through rose tinted glasses from the outset.
But the reality is, unless the boat has been "designed" first you will always be pushing a large stone up a very steep hill.

The design must be fixed - every aspect must be known in advance, as that is the SOR and target. The plans for build, are based upon the design/SOR.
The plans should cover all aspects for the build and the design intent. Making them up as you go..is a recipe for more time and costs...

Starting with herculean amounts of enthusiasm sadly doesn't help..other than being full of beans.

Your enthusiasm and perseverance really really got you through this...and is a testament to your dedication. You should be rightly very proud of this work..
But..just image if you spent a few weeks/months (as suggested ) designing and drawing up the plans of the boat first..to curb that overwhelming desire to cut something, anything just to say "...im now building my own boat.."..before embarking on the thrill of cutting wood and glassing the bits together. It is hard...because the desire to start is strong!!
However, ....the progress you would have made and time/cost savings would not be small!

Whether building in your back yard or in a modern professional shipyard... everyone needs Plans, and Plans based upon a fixed target - a design/SOR.
Know where you are going, before you start... that allows planning and budgeting of time and costs too.

Well done DC...take a large bow

 

[DogCavalry]

If possible... I had a golden opportunity to use a shop I could not otherwise afford, but the clock was ticking. The next boat I build will probably be a TX-18, from plans.

 

[DogCavalry]

Another thing that tripped me up was the fuel tank(s). Moeller makes good tanks in a lot of sizes, but none of them fit very well, so I had to get a custom aluminum tank welded up. If I had selected tanks at the beginning, I could have built them in.

 

[fallguy]

I've seen a lot of boats glassed and never or rarely transverse. So gonna disagree. Uneven ridges on bottom overlaps would require fairing to avoid drag or worse.

 

[kapnD]

There are certain techniques used to handle delicate, slippery weaves, rolling, folding, and above all cutting, marking and stacking in order all pieces in advance of lamination.
An experienced crew makes it look easy!

 

[DogCavalry]

It might have been a quirk of the biax I used. Even under it's own weight, it distorted.

 

[baeckmo]

Afraid I've got some nose-rubbing to do here; it is an extension of post no 8, so please take it positively!

You selected a hullform before knowing where your stuff was to be placed; ie you did not know if the weights and their resulting CoM would suit the selected hull shape. That is a backwards engineering procedure that may work for a displacement hull (although not optimal), but never for a planing hull that is depending on a positive angle of attack to "take off". When starting with a given shape, you must check its "balance point", and select your arrangements accordingly!

I did try to make you weigh the hull at two positions in order to get an idea of the CoM as built, but unfortunately the message didn't "penetrate". Now you have a boat with a negative trim unloaded, and with a cargo on deck it will be even more so. Continous weight control during the building process is absolutely vital; most of the forum questions about bad performance have their origin in lack of understanding of the weight issues.

One result of the negative trim is that the flow around the rear part of the hull is "rolling in" from the sides to fill the void under the forward tilting bottom. This movement is pushing the bubble cloud towards the center at the transom, where it causes the prop to "whip the foam". When starting with a positive AoA instead, the aft flow trajectories tend to diverge across the flat hull section aft, thereby flattening the bubble cloud. I made a quick simulation on a typical Hickman shape with bottom twist and flat transom edge (without free surface effects) just to demonstrate the effects, see pics enclosed.

Since the foam has lower density than the water, it will migrate to the inside of a bend; if the flow deflects towards the center, the gas will collect close to the center and vice versa.

 

[DogCavalry]

Oh, I am well aware @baeckmo . But the only movable weights on the boat are at the transom anyway.