need help with plans

Go and have a read of Murielle's Web site.

http://www.magma.ca/~ovenden/index.htm

She's got a lot of information on how they're blasting their boat.

I chose the option of sending my steel to a local industrial blaster and get it back blasted & primed. It costs me $22/m2 but I don't have to do it myself.

I do have an air compressor big enough to do blasting. It's output is 120 cfm, on the 'acceptable' side of adequate, not overkill. There's a 25HP 415V 3 phase motor driving it. This is not overkill for the work, believe me. I can't give you figures on sand etc consumption because I'm paying a place that's set up to do this. I bought the compressor so I could do small amounts of blasting and run other air-demanding tools.

My understanding is that in the USA both wheel abraded & primed and pickled & oiled plate is available but generally you need to ask your steel merchant for it. Try to see if this is available because if so, you can save yourself a lot of time, money & tears.

I'd happily pay AT LEAST 25% more for steel with the mill scale off straight from the merchant. I'd even compromise on my ideal plate sizes (but not thickness) to get it.

I think we all have gone through this disbelief-denial-cost terror-grudging acceptance cycle on steel work so don't think that I don't sympathise - I do. However you have to build from steel free of mill scale or blast to clean steel before painting when the hull is finished, both ways have pros & cons but the end result is the same.

PDW

 

PDW-what type of boat did you build?..what's the stats on her?

 

I'm still building her which is why I'm all to painfully familiar with the steel blasting issues. ATM I'm plating the hull.

I chose a Tom Colvin Saugeen Witch design stretched to just under 12m, displaces approx 7.5 tonnes. Tom did the stretch calculations and rigging plan for the lengthened hull plus the new stability calcs etc. Lot of work building but no dramas. The lines & offsets are excellent. I lofted her full scale and picked up all the frame dimensions etc off the loft floor.

PDW

 

The ONLY difference is, that you changed the entire design! That is not the way to go Mate. It just does not work, you most probably produce a *****.

Tugboats are amongst the most dangerous craft afloat! Each and every detail of the design is far more important than on a ocean going cruiser !!!

When you have a vessel at the hook, a screwed design easily kills you.

Stay with a proven design, or give that tug idea up!

Pdwiley gave you the right advice on blasting, he obviously knows what he´s talking!

Regards
Richard

 

Awesome stuff--I actually didnt know if Mr Colvin was still doing any design work?..when he had written the book i believe he mentions that he is not going to build any more boats except for his own pleasure. Ill have to go look that up. IS that sail design?..he does have some complicated ornementations ie. the spar on his pinky design and the style of stern look a bit tricky. He is definitely old school...i loved his tugboat reference for cant framing. if you have any pics--i would love to see them?
soryr my pic of the tug hull is so small...
btw i did some calcs for the hull and blasting--it appears that blasting
at $22 /m3 would cost me aprox 2600.00 which isnt bad...hope im on base with the cost figure? the boat would be about 600 square feet give or take...so i figured about 1200 sq ft inside and out roughly?

 

PDWILEY- i just called a place here that does blasting- i got a quote based on the 30 ft vessel- he told me the hull would be about 500-1000 dollars to do and about 4 hours of work...thats much less than i thought. but ill have to see if its less work and expense to buy the treated plate...

 

That is not possible to achieve! He meant the outside only, take care! even a 30ft boat interior blasting is much more than a few hrs.

 

Richard- asusming that im incorrect about the chine and how ive done the vessel--whats the worst thing that could happen?..im certain it will float..thats the first step--the second is that im sure it wont be too heavy and if too light, ballast will solve that problem...IF NECESSARY...

3rd--i know that the plate thickness is stiff enough. im using the same scnatlings as the 25 ft double chined pintle design...
I cant really see what if a any problems would be??..ive sene other deisgns with almost identical configurations below the waterline...whats the worst thing that can happen--realistically??? I just cant see any real probs with it. but im open to hearing what specific problems might be encountered??...and if necessary ill adjust it accordingly...
yes you are correct that was for outside blasting...

 

First, I don´t know the changes you made, because I don´t know the original design! But changing from round bilge to hard chine is a severe operation, especially on a rather critical vessel, which a tug is generally.
Second, I cannot lead you to a solution, I just don´t have the knowledge to redesign that given boat (or any, if you like), I am not a NA, just a builder.
Third, the scantlings of one 25ft boat can be heavier than for another 30ft craft, for several reasons. So any comment on that issue is not serious without having all the info about the vessel in question. And even then, I am not going to comment on them.
After more than three decades in business and over 40 years at sea, I would NOT design my own yacht. Though I dare to comment on designs and even force NA´s to major changes before I produce a yacht.

That was not too helpful, but it was frank, I hope you can live with it.

Regards
Richard

 

pdwhiley is correct, you cannot remove mill scale with a wire brush. Additionally, a wire brush will not leave a profile on the surface of the steel.

What this means in simple terms is that a brushed surface will be smooth and slightly polished, resulting in poor coating adhesion. By contrast, a blasted surface will have a rough profile, which is to say, a toothed surface, that your coating will adhere to better.

Hire yourself a professional blasting company, it may seem like a lot up front, but they will be done quickly, and your coating won't fall off afterwards.

I used to be a Nace Coating Inspector.....

Updated: here is a list of qualified coating contractors, most of them will blast as well:
http://www.sspc.org/links/contractor.html

 

The Witch is a stock design and has been stretched before so I don't think it was a lot of work for Tom to change. Yes it is a sail design. As far as I know Tom isn't building boats but he still sells plans and consults. He is in his early 80's as far as I can figure.

The bow on the Witch is strip plated to give compound curvature and looks lovely (if one overlooks a few hollows in mine that I need to fix...). After the bow area it's all developable plates. First boat I've built and it's going well.

The $22/m2 is PER SIDE and you really need to do both sides. Also here we have this lovely thing called GST that adds 10%. 5 plates of 3000 x 1800 cost me $1320 inc GST. I figure I'll use 15 plates by the time I'm done. As near as I can figure it would cost me $5000 to buy sufficient equipment to do the job myself, plus consumables like garnet. Problem is finding the equipment used near where you need it and then you still need to spend the time blasting when you could be doing something else. It's a noisy dirty horrible job, some things are worth paying for. You also need to be on a site where you can get away with blasting, a suburban yard isn't going to be the place and possibly nor is a commercial yard if they also have paint work in progress. There isn't a right answer, circumstances alter cases. I've got 3.5 acres of land and only 2 neighbours who both have more so I can blast (and run angle grinders for hours etc).

BTW I also would not design my own boat nor would I screw with a stock design. You would be amazed (horrified) how seemingly small changes add up to really big ones when you translate a set of 2 dimensional lines to a 3-D object. Build it to the plans, pay the designer to make the mods or I guess pay a NA to do it for you. Professional plans & design advice is dirt cheap compared to the materials costs alone in a 30' plus boat of any type. I'm definitely a DIY type and have designed/built 3 houses including a 3 storey one, but the boat is getting built as closely as my skill permits to the plans provided. Even seemingly little things add up; Tom is adamant that one not use steel for the cabin tops for example because it was designed for ply & glass and the weight of steel raises the COG. OK, you can add ballast to counteract this but now you've reduced your ability to carry stores for the same DWL. OTOH I swapped the keel shoe from 200 x 25 flat bar to 200 x 40 because I got it cheap, but I asked the designer first and got his OK. Steel is cheaper than lead and it's all ballast there.

PDW

 

Its all good Richard--i learn from everything that gets said, just one thing i maybe didnt mention was that i hadnt planned on changing from a round bilge to a hard chine or vice-versa. the pintle is actually a double chine design. but i just used a single chine for the tug hull as shown.
as you know any input is always welcome when it is in the spirit of helpfulness...I appreciate that you are frank--It gives me a good idea of the difficulties in this process- all i can say for sure now is that -In the next 20 days ill have the engine shipped up to the build site, change the transmission (an Mg 61 twin disc gear 3:1) and ill be starting the build. Ill post pics of it...humorously- At this point my wife/partner intervened and told me to stop ping ponging and build the 45 ft boat since thats the one i want...she supports me--so even though its not the boat i designed it will be sound.--ill build it from the N.A. plans as given. *but fair warning*--you may not like my choice of materials...but thats for another day and thread...

 

Hi MathewDS- yes it turns out i was in denial afterall...but i was quick to realize this fact. however --since i posted last My partner has stepped in and basically tired of my boating rants and when the women of the house decides soemthing -she usually knows better than me...anyway -ill be building the 45 ft tug- but -ill not be doing it in steel. I did check into the cost of blasting and it wasnt as bad as i first thought- about 2000.00..inside and out.

your post was appreciated!

 

PDW-ohhh we have that nasty little thing called a harmonized sales tax too! used to be GST but they merged it with the provincial and federal tax to the tune of 13%!!

and your reasons in your post which paralleled mine-is exactly why today -i sat down-took out my models of both hulls, and locked myself into a room for an hour --still couldnt decide between either two- then consulted my oracle(my partner gf). since then i have firmly decided to just build what i wanted in the first place- a stock design at 45 ft tug hull- but im not going to use steel..

i can get a close approximation of the wieghts with the materials, but ill need ballast-however I understand in some cases this is actually an asset.
and Ill be calling the design office too- but its unlikely that the office still has the deisgner from 1952 still there- however I may take the plans to a engineer. or N.A for some advice and pay for it--it cant be all that expensive-and less than sandblasting- cnc'ing curved plate and frames for a 45 radiused or round bilge hull!!
I know of a product on the market thats as strong as steel and more resistant to puncture than steel. Ill be using that instead. There will people who will tell me not to do this-that the material will need to be heavy or that the material is junk--im sorry for them because they dont knwo what i know about it...
--but -i am just a rebel--so we will see, its been a pleasure PDW- i appreciated that last post since I am a Colvin fan and owe him a debt of gratitude to understanding how a steel boat is built. I really wish he would have designed some smaller tugs...say in the 35-40 ft range. but i am very very intent on having a radius chined or round bilge tug design for economical running. I dislike hard chine designs. There was a nice plan for a 40 ft'er in steel by the MacNaughton group--but just didnt quite meet my needs. i didnt like the upswept fantail stern. maybe I could see if Mr Colvin would design a small tug for me? what do you think he would charge?

 

You're going to use Fer-a-lite I'd guess. Good luck with it. I have nothing further to contribute to the discussion, however, as not only do I know nothing about it except what I read 30+ years ago (it isn't new), I also have no interest in its use. The resale value of the boat is going to be a small fraction of a steel hull built to plan because nobody else believes in that material either.

Have fun whatever you choose because there's little other reason for building your own boat.

PDW