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Old 13-06-2008, 08:39   #1
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Replating a steel hull and deck/superstructure.

Hi,

I would sincerely appreciate some advice/ views on reconstruction replating and associated areas.
I have just cut out the first section ( 3m x 1.5 m ) of hull bottom on a 40ft steel yacht ( heritage/pedigree unknown at this stage but it is well built ). I am just about to replate in new 5mm plate.In all there will be approx 6 sections of same. As I am also replacing some frames/stringers which have thinned out at the same time.I am doing this ( frames/stringers ) more as a precautionary measure and for peace of mind also.See general photo of frames.

Existing motor was an ( old hand crank ) 20 hp x 2 cyl Yanmar which I am upsizing to a 30 hpx 3cyl Lister,elec start.Weight difference might be 100 or so kgs additional weight
Existing framing is 6mmx 50 mm flat bar.
Existing hull/sides plating is 4mm.
Existing deck/superstructure plating is 3mm-but some appears to be 4mm in some sections mainly at bow and stern areas.?

Question

As far as added weight goes -could I use 75mm x 10 mm flat bar instead of 50 x 6 for reframing where needed and as this is also being added to 5mm hull plating and new motor set up am I going to penalise the boat with the added weight or is it not going to hurt in the big picture ?
Is the 10mm thick too much.?

As I have access to quite a few 3mx 1.5m x 5mm sheets of plate am I able to use the 5mm plate on the decks( but not cabin area ) or should I stick with 3-4 mm.?
The common sense side says the extra weight should not be a real problem in the big scale of things and I will know my boat is really strong and able to withstand some pain if it needs to which is very important to me.
The undecided side says watch out for the weight.

The yacht has a long fin keel( see photo ).This will probably open up a can of worms but to get the correct final keel weight I need I am going to consider using railway line welded to the fin keel in long sections.The rail I can utilise weighs 60 kgs per metre and is what they call head hardened i.e. bloody strong. I know this is in contrast to boxing in the fin keel and placing ballast inside the keel and really outside the square but the flow around the rail section affixed to either side of the fin keel if anyone knows rail cross section may be better than flow around a boxed in keel section.To my way of thinking it will be somewhat like a winged keel but not as fancy.At least being affixed outside the hull and able to be seen/treated as needed it gives me maintenance access.
Note.I accept that my idea of using railway line may be seen as a bit too far outside the square and maybe even seem a bit loopy for all of the more experienced people out there but hey I'm a learner so feel free to knock me around a bit.I got plenty of that as an apprentice.!

The superstructure is being redesigned/rebuilt to take advantage of better layout but will be in keeping with existing design parameters.
Should the cabin/top section be kept to a 3mm plate thickness to keep the weight on top low or can 4mm be used.?

Steel angle bar for flooring/framing/structure building was/is 25-32 mm x 3mm thick in general throughout the boat overall.
Any problem in me using 50mm x 4mm/5mm angle bar down in the low section in the boat.
Again- adds weight but will it cause me problems.?

In all,if say an added weight of 250-300 kgs is added with different motor and steel plate/angle bar being used plus the keel weight will this make it sit all that lower and cause stability problems.?
Or am I actually just using better materials for the right reasons.
The flat bar and angle bar makes a difference also as I have it available to use for free and I can't argue with that first up without seeking advice.

Do I need to seek professional advice from a Naval Architect/Engineer for working out the correct weight required in the keel/lower hull area etc or is there a formula for this someone can point me towards ?

Thanks in advance and hope you can possibly point me in the right direction.

Regards
John.
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Old 13-06-2008, 14:31   #2
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Unless you are intending to go to the poles an do ice breaking, 5mm plate is rediculous. Same for frames. The weight gain would be horrendous. stick to the 50x6
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Old 13-06-2008, 15:49   #3
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By the book...

Get yourself a copy of "Boat Strength for Builders, Designers and Owners" by Dave Gerr. Amazon should get it to you in 10 days or so.

The author uses simple tables, graphs and formulae to work out scantlings for boats. It is really quite user friendly.

Boracay was built a little light. I think they used 2.5mm plate for the deck and I have not found a single part that is heavier than it has to be.

The problem with extra weight is that it is easy to get it in the wrong place - up high or in the ends.

Before you really get stuck into this please consider if you are rebuilding an axe - replacing the head and the handle.

Much of the thinking on this Forum has been that cats are more suitable for cruising than monos. You could possibly build an Easycat 37 from scratch quicker and maybe cheaper than rebuilding this boat.

My own observation is that when guests come aboard Boracay they like to sit in the cockpit. A cat is one large protected cockpit.
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Old 13-06-2008, 17:38   #4
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Using 5mm plating is adding a gross amount of weight to a 40 foot steel boat. Taking into account your photos showing longitudinal and frame spacing 4 mm would be "normal" and a mix of 3mm and 4mm on the deck (4mm where there is inadequate support to prevent the biscuit tin lid effect). As a general rule the thickness of plating on a 40 foot sail boat is driven by being thick enough to work with and avoiding the biscuit tin lid effect where the supporting spans under it are not close enough.

50x6 or 60x6 mm for frames would be "normal" for the construction shown and probably their main purpose in life would only be to keep the longitudinals apart until plating has finished - eg it is not unsual for them to buckle during plating due to the hull shrinking up during the welding of the plates. Deck beams would normally be the same as the frames but deck longitudinals considerably smaller.

I would be very careful of using other than the minimum plate thickness and deck longitudinal cross section you can get away with in way of the deck and superstructure.

A very common mistake by amateurs, especially but they are not alone in it, is overbuilding the boat and so adding gross amounts of weight and turning the boat into a slow and crank one with no useful gain in structural integrity at all.

Apart from plating thicknesses areas one often sees needless weight is in steel bulkheads (structural steel bulkheads should not be necessary in an adequately constructed 40 foot vessel - if a watertight bulkhead is wanted forward, which would be unusual in a 40 foot pleasure boat, it can be of ply with vertical timber stiffeners), installing beam shelves for the deck beams (a hangover from timber construction but unneccesary in a 40 foot steel boat, especially if there is a steel rub rail welded along the hull outside the sheerline), over building of the interior joinery including bulkheads(everything inside the boat only has to support itself, it is not part of the structure and is also not subject to wracking as small steel vessels are very stiff), use of steel framing for any part of the interior joinery including for supporting the sole (is no need for steel).

Personally I would forget about welding railway rails to the outside of the keel for ballast and do it in a more conventional way (you may be able to use the rails cut up and placed inside the keel with interstices filled with steel punchings, then all encased in concrete if the keel interior volume is great enough to get the required ballast mass without going to lead) - if there is any uncertainty as to the amount of ballast required I would strongly recommend getting some professional advice.

Unless it is a labour of love to restore the vessel (which in my book is a valid enough) I would, if it were me, consider scrapping what you have got and starting from scratch. The material cost in the hull is a small percentage of the total construction cost and I suspect that the labour to rebuild what you have, including assuring future useful life of the result given the extent of internal rusting of the hull in way of under longitudinals, etc (which blasting will not remove and interior rust ultimately determines the useful life of the boat due to the difficulty of removing it) will be considerable. You would also end up with a modern design chosen for your exact needs.

Whatever you end up doing I suggest, if not done already, making up a complete budget for the materials, equipment and your own labour to complete/build the boat taking advice from those who have done it before. It is a much bigger job than most appreciate.

With respect to labour, assuming a reasonable level of finish and interior quaility a professional yard would probably budget around 4,000 man hours to build a 40 foot steel boat (is normally about the same as for a timber/glass composite boat due to the greater amount of work in way of insulation and linings in a steel vessel), so approx 2 man years, assuming all the normal equipment such as rig, deck hardware, etc is bought in rather than fabricated on site. Less hours are required for a very utilitarian boat if that is what is wanted.

John
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Old 13-06-2008, 19:35   #5
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Listening intently.

Midland One,
Thanks for the extensive and no doubt well thought out reply/advice.
I was half expecting that the general advice on the plating thickness would be caution.The 10mm framing was only to be considered if the consensus was with most and then only say every third frame if actually needed,but I see the sensibility in this in sticking to the norm 5-6 mm.
The existing hull plating is 4mm so I thought 5mm would not make a huge difference.?The existing deck plating is 3-4 mm also.?
Note: The 5mm plating was only to be used on the bottom of the hull unless advised otherwise.Happy to go to 3-4 mm elsewhere if that's what the consensus is.The pictures you have seen really make the boat look like a dog but in real life it is a different picture.The rust you see is simply from holed decking letting rain in due to very poor maintenance/vandalism.

Also as I am going to be sandblasting fully internally/externally I believe the exisiting rust will not present too much a problem but again happy to take advice on that issue.Will the sandblasting not get right in and under the longitudinals ??

It does take some getting past what I am taking on but I keep reminding myself that this exisiting hull is fairly sound,wellbuilt even if old and has only cost me to date $2,500 including the purchase of the 5mm plating.The Yanmar motor/gearbox that came with it can be onsold also. Given that there are 15 sheets, what I dont use I can probably sell for around $250 per sheet which is approx 50% of the cost of a 3m x1.5 m x 5mm sheet, steel being what it is at present.
Maybe I should scrap it but I am finding it hard to consider given the low cost to start with.
I do have one of the best welders around my area who is going to help me so that gives me confidence.Being 52 years old this boat will probably only see me going coastal sailing /motoring ( by the time it is finished anyway !! ) so it does not have to have all the whiz/bang electronic gismos straight away.

Points well taken and will heed on the keel and internal fitout side.

Boracay,
As usual,well placed advice.Thanks very much.

Alan,
Thanks.
Definitely not going anywhere near the pole.!!I am a warm water type for sure.Advice heeded on the 50x 6.
Will 1mm extra for bottom hull sheets make all that much difference though.See the point in not using on the top etc but I thought that the weight might help on the bottom end ?

If the general consensus reaches a crescendo I will consider scrapping it but my heart is really in this.Might come back and haunt me till my dying days but something tells me this boat has got some real soul left in it.
Maybe I am just a hopeless romantic who likes to recycle rust ?

God help me !!

Regards and Thanks
John.
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Old 14-06-2008, 00:49   #6
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Yep, 1mm makes a big difference. Many hulls are built with just 3mm high tensile steel.
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Old 14-06-2008, 05:39   #7
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Quote:
Originally Posted by john connell View Post
this boat will probably only see me going coastal sailing /motoring ( by the time it is finished anyway !! ) so it does not have to have all the whiz/bang electronic gismos straight away.
G'day John,


Although I've never personally built a ship/boat, I've seen what's involved when dealing with ship/boat yards during the maintenance of trawlers/trollers I worked/operated on & would agree with MidLandOne's 4,000 hrs figure.


If on average you work on the boat 45 out of 52 weekends p/a then it would take you 3.7 years to complete 4,000 hrs (24hrs p/weekend). I do note that the quoted 4,000 hrs figure is for professionals that are already used to & prepared for all the complexities of boat building, therefore an amateur could exceed that number by a significant factor.


Having said that, I've seen boats built whereby the builder completes the hull, superstructure, painting, engineering & plumbing, yet the owner completes the fitout. Perhaps this might be of interest to you? This at least would give you a floating motor boat until you complete the fitout & rigging. Also note that hull's can be built economically if done as single chine, raised sheer, no fairing & flat paint. Furthermore, builders can get oem pricing on marine parts.



Quote:
this boat will probably only see me going coastal sailing /motoring ( by the time it is finished anyway !! ) so it does not have to have all the whiz/bang electronic gismos straight away.

Electronics are very important inshore where most of the traffic & shoreline is.

I admire your energy & wish you luck on your project.
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Old 14-06-2008, 07:18   #8
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Hi Exfishnz,

Yes you are perfectly correct re the electronics.What I meant was I can probably get by with some lesser expensive units whilst I save up for the better ones.

Another positive point is that I am extremely lucky to have the boat on a hardstand with power ( single and 3 phase ),water,a 20 x 10 mtr adjacent carport with concrete all around the boat.I have a large workshop 50 ft away ,can make as much noise as I like 7 days a week and it is 5 minutes from home.All for $30 dollars a week.One of the blokes on site has a crane truck,another has a industrial high pressure cleaner /sucker truck.
Blessed is more like it.!!

My actual trade for the last 35 years is as a Plumber/Drainer /Gasfitter ( LPG and NG ) and Roofer.Dont play in that field now but still hold all my licences.Have a very good marine welder coming to help me/teach me and also have had a fair amount of experience in designing /fitting out kitchens /bathrooms,tanks etc.
Not scared of a bit of hard yakka.
Due to a very flexible organisation I now work for also have the ability to take off a " bank" of time,say 4-5 days straight on top of normal leave.
This boat is a single chine.She has some plate sections that are crap but the rest of her is really,really solid.

Frankly I dont know why I keep defending her- she looks scary in her present state and I should be running away at knots but I can't-I'm hooked like a bloody drug addict.
You might have to come and visit me in the funny farm soon but I will always remember your advice.

NB. I know there must be a really good reason but I wish to understand why 1 extra mm will make such a huge difference to the hull plating if the existing/original plating was already4mm.
How much extra weight will 1mm over say 24 square metres add ?

Can anyone give me the goods on this.?

Regards and Thanks.

John
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Old 14-06-2008, 07:42   #9
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How much extra weight will 1mm over say 24 square metres add ?
Check it out :

Weight Calculators - Weight of a Steel Plate - Chapel Steel
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Old 14-06-2008, 11:26   #10
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Go for it. I would recommend that you get Dave Gerr's "The Elements of Boat Strength" as someone previously mentioned and then go for it. One mm on the bottom of the hull will only mean maybe 5 kg. less ballast in the keel, if that. Heavier topsides though is not good. Using the right steel is more important than using steel 25% thicker, IMHO. Larger stringers will add what, 50 - 100 k. overall. And again mostly low. Replace one 3/4 in. plywood bulkhead with a foam core epoxy bulkhead and you will gain that weight back. Of course I am just guessing at the weights here so do a calculation of the added weight keeping in mind where it will be placed in the boat and go for it. Good luck and keep us posted with pictures as you progress.
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Old 14-06-2008, 16:33   #11
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The "More is better" school of thought met its demise in boat and airplane building. Did you know that the main reason for going from wooden hulls to steel hulls was to save weight? (and to save money, trees that big were getting to be very rare and damn expensive!)
While dreams are wonderful things, boatyards all over the world are full of mouldering projects that might have become transports of those dreams, but ran full square into realities the builders might have been warned about.
If this boat is going to sail, a lot of thought needs to go into its rig and vessel dynamics before any fundamental structure is added or removed.
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Old 14-06-2008, 21:21   #12
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Food for thought.

Hi,

Morgan Paul.Thanks for the link-perfect.

DeepFrz,

As I see it going for the 5mm as per against 4mm for bottom hull plates will add aprox 88 kg weight.
Being down low just above keel your suggested advice on less need for the ballast does make a lot of sense.The new 40 hp Lister in place of the existing 2o hp Yanmar will also have to be considered weight wise.
Think I will stick with general advice for the 50x 6 frames though as this makes perfect sense but I may be able to use the 75x 10mm for a few well placed stiffeners ( say every 4 frames if any need replacing as I go as long as I dont go too wild. Any stringers that I need to replace I can cut down the 75x 10mm flat bar I have been given for free with my trusty plasma cutter.Topsides is where I think where all agree it is prudent to go less is more.I will seek professional advice here.The foam core epoxy idea makes perfect sense.
Will be ordering the book that you and Boracay advised is good value.Thanks.

Sandy,
Good advice thanks.I have been skirting around the edges getting some general advice in regards to rigging,masts and the dynamics side of it.Now I am getting some invaluable help here within the forum with the other type design parameters it is assisting me in being a little bit more confident.
If this boat gets say an added extra 250-300 kilos with the extra 1mm plate, different engine weight,etc I want to know it is going to sit right,motor and sail right and come back upright if it ever goes over.Having said that I know nothing much about building boats.
To me common sense has always been a yardstick I try and use daily. Your comments are basically what I see as "chapter and verse" common sense
Even my brother who has been a very well respected civil engineer for 55 years sometimes loses "battles" with me over fundamental design or construction issues.
Cause.? Common sense.
You just can't argue with it sometimes-it works.!!

That's what I was looking for here in the forum and I am getting it in spades.The differences of opinion open up your mind for more investigation, sometimes amazing in their simplicity and well meaning.

Regards to all and thanks for your imput.

John
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Old 18-06-2008, 01:24   #13
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If this boat gets say an added extra 250-300 kilos with the extra 1mm plate, different engine weight,etc I want to know it is going to sit right,motor and sail right and come back upright if it ever goes over.Having said that I know nothing much about building boats.
Your entire post is excellent John, most especially what I quoted from you.
Weight, or saving of it is important. But more important is where the weight is placed and how that influences motion of the boat.
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Old 18-06-2008, 03:33   #14
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Workin it out.!! just plodding along with help from all angles.

Alan,
Thank you kindly for the compliment.What makes it excellent though is the valuable input ( priceless! ) and passion you guys offer up to people like me.Reading all types of books about boat building helps out but reading about practical experiences from a first hand perspective is much better.
Must admit I have wavered a few times in my mind about this project since I have read some of the feedback/advice but in the end the confidence you guys have given me weighs better on the positive side to go forward.

So- No looking back now.Will try and make a half baked journal of it as I go and will post a couple of befores/afters just enough to not drive anyone too mad.
Maybe some day after I have finished this ( or even half way through it ) I can repay the favour to another "apprentice" who comes along asking "newbie " questions.

For now there are way too many questions burning holes in me.

Regards
John.
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Old 18-06-2008, 10:11   #15
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So- No looking back now.Will try and make a half baked journal of it as I go and will post a couple of befores/afters just enough to not drive anyone too mad.
Are you kidding. Just about everyone here is a boat junkie, so don't worry about posting to much...<gr>
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