Construction Methods

westernman

westernman

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What are the advantages and disadvantages of different construction materials for a heavy displacement 50 ft or so sailing boat (pilot cutter style).

1) GRP
2) Traditional wood
3) Wood+Epoxy strip planked
4) Steel (radius chined, hard chined just looks to ugly to me)
5) Ferro Cement
6) Others?
 
Boats of that type have been built using all of those methods, so I guess there is no right answer!

The characteristics of each are well known, endlessly discussed, but in the end the choice is often down to personal preference - after all it is paid for by the person who commissions the boat so he has to be right!
 
QUOTE.
What are the advantages and disadvantages of different construction materials for a heavy displacement 50 ft or so sailing boat (pilot cutter style).
END QUOTE


1) GRP
Less maintenance.

2) Traditional wood
Lots of maintenance.

3) Wood+Epoxy strip planked
Light and strong, good for one off designs, normally have GRP covering.

4) Steel (radius chined, hard chined just looks to ugly to me)
Not a lot more maintenance than GRP provided you get any chips sooner than later. May have more problems with condensate in some climates/conditions.

5) Ferro Cement
Can be expensive and difficult to insure and difficult to sell later.

6) Others?
Composite, a bit like strip plank but using closed cell materials like foam or Klegacell. lighter and strong, but avoid the construction below the waterline, use solid glass and epoxy.

There is a form of strip plank also that does not use timber, rather more like pre cast planks of foam and glass that are edge glued, makes for rapid build time.

Having spent a lifetime around boats and repairs:
I do all I can to avoid any timber on a boat, none at all is best. never use ply backing anything or Balsa cored.

I never use any core material that is not 'closed cell'. This ensures the internals will never turn into a slush as is often the case with rudders and some hulls.

Always look for designs that have a bulkhead both ends of the engine compartment and you will never have the stench of diesel in the cabin/s.

Good ventilation is a critical item in any climate.

Hope this helps.

Avagoodweekend......:)
 
I notice that aluminum has not been mentioned yet. For a custom build it would be my first choice. Strongest low maintenance material, totally dry bilge as every fitting is either welded to the deck or blind tapped into welded doublers, quietest and warmest if insulated properly. Watertight bulkheads and thicker plating in vulnerable areas for crash protection with flotsam are easy to incorporate. Painting above the waterline is optional. If wired properly with care and double pole breakers there should be no issues.

My second choice would be modern cold molded/epoxy construction. Lighter than single skin fiberglass and less maintenance than a glass boat. Blistering is not an issue and the warmth of a wood interior.

Fiberglass would be my third choice. Solid glass hull and deck cored with Nida-Core and no balsa.

Ferro-cement is a fantastic material and were I planning a houseboat on a barge or a in ground swimming pool it would merit consideration. But not for a boat.

Steel has too much maintenance for my liking and carvel wood is not in the running for the same reason.
 
A new boat construction

I think fibreglass is a magnificent material for long life and minimum maintenance. It also is very good for coping with total neglect.
However if you are thinking a new boat then you need to look at total cost versus resale value.
Concrete is ruled out as being very difficult to sell. Somewhat similarly epoxy on ply and steel.

In fact the best financial deal is to buy second hand polyester fibreglass. If you want new then buy a well regarded hull type and fit out yourself. Both these plans having a product with the best resale possibilities. (and probably the most satisfying result for yourself).
I once heard that a new boat costs aprox 1/3 for the hull 1/3 for the sails and rigging and 1/3 for engine and equipment. At that rate why try to save money on the hull when it is the very essence of the boat. (especially for resale) good luck olewill
 
mitiempo said:
I notice that aluminum has not been mentioned yet. For a custom build it would be my first choice. Strongest low maintenance material, totally dry bilge as every fitting is either welded to the deck or blind tapped into welded doublers, quietest and warmest if insulated properly. Watertight bulkheads and thicker plating in vulnerable areas for crash protection with flotsam are easy to incorporate. Painting above the waterline is optional. If wired properly with care and double pole breakers there should be no issues.
Click to expand...


Your right, aluminium has not been mentioned.

I recall a horrendous deliver from Brisbane heading north in a brand new alloy fishing boat.

The proud owner was on board and wanted enough crew to run non stop for 3 days.

The sad news was the new 2 stroke diesel fitted, the boat being all but empty rang like a bell, I was the person on board with ear muffs and a supply of ear plugs. Even with muffs and plugs it was impossible to sleep, and even if it had of been the condensate forming inside and trickling down the walls was constant problem.

After 2 days we just had to stop and all get some proper sleep at anchor, under way again 9 hours later.

He had some major problems after the delivery with stray currents and anodes in the marina, had to replace some underwater parts at great expense. He also gave up on trying to stop the paint falling off and the many areas that turned white and powdery.

All that was about 10 or 12 years ago, he now has a 15 m fibreglass rig.

Avagoodweekend......:)


.
 
What boatbuilding stuff

First you have to say where you are in the process,building,commissioning or just buying, and what you want it for.
Then you provoke a good(or bad) argument (like the current Bavaria thread) once they start slagging each other off you have to use your head as there will be lots of exaggeration but in the end the advantages/disadvantages will emerge.
However since posters on here have to defend their current investment you will find that the bias will be in favour of grp.
 
Quandary said:
.....However since posters on here have to defend their current investment you will find that the bias will be in favour of grp.
Click to expand...

Perhaps Quandary.

I own a 41' GRP boat from the early 70s. Bought because I knew the boat and it was affordable.

My first choice is a marine ply 40' Wharram Phai "Captain Cook". Easy maintenance and modification but I would want to build it myself as you just don't know how they have been put together. Nearly all are self build and the professional builds are just too expensive. Building takes too long. So rejected.

Second choice. Hard chine steel. Strong and can take a reasonable ramming without puncturing. Very survivable hulls, not considering other aspects. Easy to repair hard chine as round chine is difficult to make. Again the good hulls are expensive but the affordable hulls required too much maintenance. I would want a new build steel but can not afford it or want to wait until I can. So rejected.

My GRP boat is strong and I can do most upgrades and repairs myself without worrying about specialist coatings. Epoxy bonding is easier than welding. GRP was by far the fastest way of being on the water for the size and price that suits me. Realistically, for me, I will have a better boat in a few years from GRP than I would with a steel hull requiring the same TLC.

Assuming you want to get on the water fast and at a reasonable cost, my advice is to buy GRP as it is a common material, a relatively stable material and an easy material to work with.

Why I choose a GRP sloop: Safe, comfortable cruising, low cost easy maintenance, available at the time I had the cash.
 
Last edited by a moderator:
Reply to Blowing old boots
6) Others?
Composite, a bit like strip plank but using closed cell materials like foam or Klegacell. lighter and strong, but avoid the construction below the waterline, use solid glass and epoxy.


I notice either Najad or Halberg uses Balsa core BELOW the water line. All of those swedish expensive boats use a core of some sort. I am not sure that I like it - Can you be sure of water integrity for 30 years????? Its bad enough, but probably necessary on decks to keep a flat structure rigid enough, but underwater - its just a way of saving weight to increase light wind performance.
 
Cored materials

Cored structures are stronger for a given weight.
A simple example is a flitched beam or an RSJ, if you separate the structural layers(as long as you ensure they are effectively and permanently connected) you massively increase the moment of resistance to bending.
That is why an RSJ will carry many times the load of a bit of flat steel of the same weight, it works well with bonded materials too. Another example, Alucobond cladding is only two layers of thin aluminium either side of closed cell foam but it can be used for large external panels, it is very expensive but saves a considerable amount of building supporting structure.
Balsa and foam sandwich has been used in boats for for about 30-40 years with few failures so far, and most of these are caused by water penetration through edges of hatches fixings etc. therefore mainly a problem in decks.
 
michaelchapman said:
What are the advantages and disadvantages of different construction materials for a heavy displacement 50 ft or so sailing boat (pilot cutter style).

1) GRP
2) Traditional wood
3) Wood+Epoxy strip planked
4) Steel (radius chined, hard chined just looks to ugly to me)
5) Ferro Cement
6) Others?
Click to expand...

Michael, despite my somewhat flippant earlier reply, I am intrigued as to why you are asking the question. You already own a boat of that type built using the current method of choice, and considered by many to be the ultimate in development of the type.

To try and answer your question, for your type of boat some methods are ruled out. Steel and aluminium are difficult materials to form into the shape of your type of boat and also difficult to finish in a way that suits the style of boat. Their general pros and cons about maintenance are well known. GRP constructed in a female mould is a strong contender, but its advantages of flexibility in designing strong, light strucures that can be replicated using automatic of low skill labour processes are of little value in heavy one off or limited run construction. The tooling up costs outweigh the production cost savings unless a significant number of identical hulls is required.

So we are left with either traditional wood or composite. Traditional wood is attractive because the hull shapes were designed to use the characteristics of the material - long sweeping curves of the planking and heavy built up frame structures. The drawback now is the availablity of the right quality wood in the right sizes (Oh to see full length pitch pine planking imported from Russia in the early 1900s!) and the shortage of skilled labour (hence high price) capable of building in the material. There are of course a small number of people such as Luke Powell successfully building boats this way and enough customers to keep them busy. Boats like his are much better built than the originals which only had short life expectancies so should not suffer from the same high level of maintenance.

However, composites are a viable alternative to traditional as they have many of the advantages of modern materials while retaining the possibility of replicating the aesthetics of the original. Ferro has advantages in potentially low cost - but weight, difficulty of getting a good finish and most of all poor acceptance in the market rule it out. So a composite is the material of choice - usually with a wood core. It is relatively easy to construct, does not require large pieces of scarce wood and can be made low maintenance. It is inevitably more expensive than a hull out of a mould, but the expense is common to all one offs or short runs, whatever the material. The only real unknown is the long term life, simply because most boats using this method are less than 30 years old. In that time a lot has been learned about the material and the failures of some of the early boats (particularly resulting from water getting in through fittings) can be avaoided with good detail design and careful construction.

So, the answer to your question is really no different from my original, except it is arrived at by rehearsing some of the arguments considered by potential buyers of such boats. Traditional and composite are the dominant methods - I don't know the split, but as the overall numbers of such boats being built is so small it is probably irrelevant anyway!
 
Chris_Robb said:
Reply to Blowing old boots
6) Others?
Composite, a bit like strip plank but using closed cell materials like foam or Klegacell. lighter and strong, but avoid the construction below the waterline, use solid glass and epoxy.


I notice either Najad or Halberg uses Balsa core BELOW the water line. All of those swedish expensive boats use a core of some sort. I am not sure that I like it - Can you be sure of water integrity for 30 years????? Its bad enough, but probably necessary on decks to keep a flat structure rigid enough, but underwater - its just a way of saving weight to increase light wind performance.
Click to expand...

Its a good point and thanks for raising it here, but are all hulls from the 70s made that way? For example, Rivals and Nicolsons may be solid GRP laid up hulls? I don't know if they are for a fact but I am pretty sure these two models are solid GRP, so very likely their hulls are more durable than what you suggest for a Balsa core hull.

This is interesting. Could anyone comment and expand on Balsa cored hulls? It would make a good addition to this thread.

Best regards
 
BlowingOldBoots said:
Its a good point and thanks for raising it here, but are all hulls from the 70s made that way? For example, Rivals and Nicolsons may be solid GRP laid up hulls? I don't know if they are for a fact but I am pretty sure these two models are solid GRP, so very likely their hulls are more durable than what you suggest for a Balsa core hull.

This is interesting. Could anyone comment and expand on Balsa cored hulls? It would make a good addition to this thread.

Best regards
Click to expand...

The swedish boats used to be solid laminate, but in the interests of improving light wind preformance, they started using cored products, which obviously are vasty stronger weight for weight than any solid laminate. I know of 1 of the these quality swedish boats (less than 3 years old) that was written off after a new skin fitting was cut in to the hull, and out poured a slush of balsa. The owner (a barrister) subsequently had to sue for recompense, and settled out of court but with a gagging agreement.

Quandary, in a reply to my post, has suggested that cored hulls have not had problems. That is probably correct, that is, until they get water ingress into the hull from an accident, or pooly sealed fitting. So I fear that this is probably a much more common problem. Viz Oyster Lightwave etc.

As you say, it would be useful to hear more information on this. I know I am very prejudiced against this for of contruction, mainly on the question of the long term durability.
 
Chris_Robb said:
I know of 1 of the these quality swedish boats (less than 3 years old) that was written off after a new skin fitting was cut in to the hull, and out poured a slush of balsa. The owner (a barrister) subsequently had to sue for recompense, and settled out of court but with a gagging agreement.

Quandary, in a reply to my post, has suggested that cored hulls have not had problems. That is probably correct, that is, until they get water ingress into the hull from an accident, or pooly sealed fitting. So I fear that this is probably a much more common problem. Viz Oyster Lightwave etc.

As you say, it would be useful to hear more information on this. I know I am very prejudiced against this for of contruction, mainly on the question of the long term durability.
Click to expand...

You certainly are making your prejudice obvious, I can imagine soft wet cores but ---'out poured a slush of balsa' ???
The first boat I had with a balsa cored deck bought new in 1975 is still Ok and sailing away as are both the Sigmas I owned subsequently. The risk of water penetration is likely to be greater where there are holes, ie deck areas, topsides have very few penetrations and while foam core was once used down to the keel area balsa is generally not used below the water line, in this area stresses are taken by frames, stringers etc.
It is cheaper and easier to mould hulls in one layer but quality builders are looking for a combination of high strength with lightness particularly above the water line.
However cored laminates can be less resistance to impact, particularly point impacts. This is why the top layer of decks is thicker than the inside. I have seen small areas of wet balsa, around badly fitted turning blocks. Where end grain is used, the small short voids do not usually conduct it far, so your 'flowing slush' must have been placed the wrong way.
There are downsides and bad practice for all methods of construction and having taken the deliberate decision to invest in what I regard as a quality boat which includes end grain grp balsa sandwich I am prejudiced the opposite way to you. However avoiding it entirely would reduce the range of plastic boats considerably.
 
Tranona said:
Michael, despite my somewhat flippant earlier reply, I am intrigued as to why you are asking the question. You already own a boat of that type built using the current method of choice, and considered by many to be the ultimate in development of the type.
Click to expand...

Just thinking about what my perfect boat would be like in case I win the lottery tomorrow :D
 
michaelchapman said:
Just thinking about what my perfect boat would be like in case I win the lottery tomorrow :D
Click to expand...
Problem with having sufficient money to worry about such things is that reason goes out of the window. Have recently looked at a custom built boat that just happened to be composite - cedar strip, khaya veneers and glass sheathed from a well respected designer, but advanced for its time, built by an equally well respected yard that is supposed to have cost £600k about 15 years ago. Went for around £100k and it wasn't a wreck. Just that getting ones "ideal" boat is enormously expensive and not valued in the same way by others!

Thankfully there are people around prepared to spend (waste?) that kind of money as in this case some of the ideas in the boat have now become mainstream. However, many of the features evoke comments such as "why on earth did they do that!"
 
oldsaltoz said:
Your right, aluminium has not been mentioned.


He had some major problems after the delivery with stray currents and anodes in the marina, had to replace some underwater parts at great expense. He also gave up on trying to stop the paint falling off and the many areas that turned white and powdery.

.
Click to expand...

My first fishing vessel was alloy. It was a great boat and probably still is. The problem was that most other boats are not alloy and I had problems when "parked" next to fibreglass or timber vessels. Their antifouling paint was never compatible with mine. Also had trouble keeping paint on topsides as oldsaltoz mentions. I should have kept it bare alloy.

Ebay at the moment has this alloy yacht hull for sale in my local area, beautiful quality.

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=170422817164&ssPageName=STRK:MEWAX:IT

The used yacht market is the best indicator of what is ideal with the usual exceptions. Best seems to be stock fibreglass, then stock sandwich glass, double diagonal composite, strip plank composite, carvel timber, steel, concrete. Concrete seems to sell but very cheap. I would hate to be trying to sell steel at the moment, the prices have dropped enormously.
 
If you're buying used there are 100's of fiberglass boats to choose from for every aluminum, steel, or composite boat. If on a budget this is the way for most to go. If you're custom building your budget has to be a lot bigger regardless of material. If you're custom building also fiberglass doesn't lend itself to one-off construction as well as other materials. It's best for series production. This is where composite wood/epoxy and aluminum become more feasible. The hull and deck are about 20% of the total depending on equipment level so the cost difference is not much when the total is considered. All gear and wiring and interior finishing will cost the same in any material.
 
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