Posted: Thu Sep 22, 2016 1:15am

Probably sounds like a silly question but would like guidance. I have been asked by my builder do I want to go for 12 mm instead of 10mm for my hull. will this make a big enough difference in the scheme of things to make it cost effective. I have apparently been made an offer by steel people at a good price.

Posted: Thu Sep 22, 2016 7:14am

I can assure you that it is not a silly question. The only silly question is one that is not asked but an answer is required. Much depends upon the quality of the steel and other factors. A 12mm base plate will be heavier than a 10mm one so the hull will need less ballast. This will allow the builder to fit a lower floor if he chooses so if you are tall it would give a greater headroom, especially important if the design has any side passages. Steel comes in a number of grades and some probably come with no grade at all. Unfortunately I do not know enough about the various steel grades to give you BS or EN numbers. The thing about graded V ungraded steel is that with graded steel there is a far better chance of the quality being consistent. This means that a choice between 10mm graded steel suitable for hull work V 12mm ungraded steel may make the 10mm a better and possibly longer lived option. I fear you will need to do research into steel grades. Springer boats were originally built with the equivalent of 4 or 5mm base and many are still in use maybe 40 to 50 years later. Dutch motor cruisers are often built from 6mm steel while 6 or 8mm base plates have been very common in the past and they are still in use, some I believe on hire boats but the hire boats have probably had work done to reinstate the wearing edge of the baseplate. Typical hull specifications are 10mm base, 6mm hull sides and 4mm cabin sides and roof. It is almost certain that the 6mm sides will require plating long before the 10mm base, especially if you do not keep the hull coating in good order. If the steel quality is the same 10mm is perfectly adequate but 12mm is nice to have, especially if you are tall, and as so many people think thickness is all that matters will probably give you an advantage when it is time to sell.

Posted: Thu Dec 01, 2016 1:57pm

I might be in a position to help regarding the steel generally used by the NB builders. As a rule the mild steel used in construction will be produced to BS EN10025 Grade 275 and should have been supplied with a Mill certificate that details both chemical and physical properties. Steel that has been supplied without a QA certificate may well conform to the standard grade but is lacking the relevant paperwork. There are no significant differences between the price of certified and uncertified steel. Now the words of warning. There is currently steel on the UK market that has come from China, and was produced with an added boron content so it was able to be classed as an alloy for export reasons. This steel has been widely rejected by the main Steel Fabrication industries as there are potentially problems with the welds cracking in certain circumstances. All you need to do is ask your shell builder to provide the Mill test certificates that are readily available, just to give you peace of mind.

Posted: Thu Dec 01, 2016 3:10pm

Many thanks for that vital information. I hope it is in time to save the original questioner from a mistake.