Jump to content

alloy hulls


Guest

Recommended Posts

hey please can any one shed light on the advantages of an alloy hull? i presume that this is an aluminium hull. Are there any disadvantages?

Link to post
Share on other sites

http://crew.org.nz/forum/viewtopic.php?f=6&t=17132

Quite a few comments here.

 

Advantages = Lightweight

Easy to bend, shape and polish; Easy to drill, tap when fitting out vs harder steel.

does not rust easily

 

Disadvantages = Make sure correct welding rods used

Make sure load spreading triangles at EVERY junction.

Electrolysis & anodes required, best several bow, stern, P&S shoulders & quarters when is strange ports / marinas; alongside steel boats, barges & fishing boats.

 

Specialist & skilled workers (= cost) for repairs vs steel where even the smallest remote island has somebody with gas bottles who can cut and weld steel.

Link to post
Share on other sites

Aluminium gouges and tears easily, although it is still a strong material.

It is very noisy. Far more wave slap comes through the Hull and the real biggy, is the sea temp is transmitted through the hull very efficiently. So the boat can get cold(or depending on what water you are in, Hot) and it is not easy to counteract that. In other words, in cold water and climates, a heater can struggle to keep the boat warm. Steel is not as bad because it is no where near as good a conductor of heat. Some insulation can be of benifit with Steel, but with Ally, you need to insulate every square inch, which is next to impossible. It simply absorbs the heat out of the air.

You need magnesium Anodes, which are not cheap nor as easy to get hold of. Corrosion can be a big problem. One biggy is what type of ally the boat was biult from. Was it a proper Marine grade or something else. Not something you can easily find out about. If biult in NZ, it would be fairly certain to say it is a good marine grade material, but overseas biult hulls, you need to be wary of, unless it is biult proffesionaly from a recognised biulder.

We looked at one Ally Hull before we bought what we have. I don't know if it was just the design or a poorly biult boat or that it was so light, but it bobed around under my feet like a cork and felt very uncomforatable. The French love them, and you will often find them in the yards sorting out corrosion issues during their stop overs. You can easily recognise them, they will have all sorts of weird and wonderful apendages on the rudders and keels and so on.

If a Hull is painted, then it needs to be done properly to ensure a long term adhesion and I am yet to see any that really has lasted. The result is a masive job of preparing and repainting. It is far better to leave the Hull unpainted. The ally lasts just fine for years unpainted. But the only problem I have with that is that the Hull always tends to look a little "workboat'ish".

As Paul has said, it is not quite so easy to repair. You need plasma to cut it and MIG or TIG to weld it, along with the proper welding Gasses. Although there are now Arc rods available, but I would be worried about how easy they are to obtain. Maybe worth carrying a packet or two as spare parts. I have not used them myself, so I have no idea how easy they are to use. Marine Ally is not so easy to bend. It is very hard and can even snap if bent tightly.

Link to post
Share on other sites

Wow that is a pretty negative list there allan, As one who has one, I would say that basically they are no different than any other vessel, yes you have to be careful with the wiring, no you don't have to paint them ,antifoul excepted, they are no noisier than a steel boat the temperature between a steel boat and an alloy one from water temperature will be identical. Any good steel boat will be insulated from the waterline up exactly the same as an ally one, So internal temperatures will be very similar, If you wish to venture to the tropics good ventilation is a must whatever the hull material. Zinc annodes work fine, magnesiun is generally suggested for fresh water useage, havn't met anyone who uses them in salt water. you don't need a lot of zincs, you can do a simple test that will tell you if you are over zinc'd or not. I have 2 annodes and was borderline over zinced.

The rollyness wheels mentions will be from the design, not because it is made of aluminium. The have their weaknesses as well as strengths as do all boats, would I buy another one? in a heartbeat. NZ has a reputation for building sound commercial alloy boats but not yachts, not sure why, Alloy yachts Ltd. excepted, Mc Mullen and Wing built a few but most others have been one offs. The French have been building them very successfully for 50 plus years, using the best materials available at the time, ours was built in 1979 from 5mm plate, at last hull survey it was still 5mm. Go to and look at some of whats available it will open your eyes as to the range available. Not cheap but tried and true. Outside of the hull they are just the same as any other yacht, only criterion is all wiring to be earth return. Don't be daunted by the nay sayers who generally only have anecdotal experience, never having owned one.

Link to post
Share on other sites

Aluminium can be cut with anything that can cut wood, Skill saw, Jig saw, band saw, 125 x 1.6mm thick cut off discs, and of course plasma, it can be planed with an electric plane, rolled, wheeled, or beaten to any required curve, welded with Mig, Tig, Stick, or gas, easily shaped, light and clean to work with, limited heat distortion compared to steel when welding, NO rust. If using dissimilar metals use an isolation shim and lanocote or something similar on SS fasteners, makes it easier if you ever need to undo them as well. :D :D :D

Link to post
Share on other sites

There is a reason that almost all newer workboats are alloy - its a very durable, tough material for a boat to be made of, with the major advantage of it being very light. I know of several people with 35' - 45' launches, and the fuel consumption, speed and maintenance costs of them are enough to make anyone with a grp or steel launch weep. And modern manufacturing processes allow them to be finished to a very high standard.

 

As for the paint - well, Wheels may have had bad experiences with them, but I have seen several which were built in the 90's and the hull paint is still very well attached and in very good order. Given a cut and polish, they come up looking very good. Actually better than quite a few GRP's I have seen!. however, some of the launches I have seen which were built with costs in mind dont look so great.

 

To be fair, all the alloy yachts I have been on or seen up close have been built by Alloy Yachts - and maybe the quality of the product they turn out has swayed my opinion - but I would happily own a good one. As long as you understand the beast, its a good one. Really, its the same as ferros - a good one will be a very good one, with the added bonus of being very light weight.

 

Alloy will tear ( so will GRP of course ) and maybe a prudent alloy owner would school themselves in working alloy, to a sufficient level that they can instigate suitable repairs. And carry a baby tig / plasma unit. Hey, aint the the same story as most blue water cruising owners?

 

I think that alloy boats can suffer terribly from noise ( and temp ) if they are insufficiently insulated. However, again, the ones I have been on were all well insulated, and indeed, because the insulation was taken very seriously, they can often be quieter and more thermally stable than other materials in my experience. I have also found that steel and ferros can turn into utter hellholes in hot environments, because once that material is hot, it has massive amounts of latent heat, which then slow roasts you as you try to sleep.

 

And Wheels - yes, compared to your boat, any light displacement boat will bobble around a lot. a ~20 tonne 45'er is going to be a lot more resistant to moving around than a ~10 tonne 45'er. Thats one thing that ferro boats really tend to excel at in my experience, but then, they also are almost always the heaviest displacement for the size that I have been on too. Tahitians are very stable boats, one of the biggest positives about them in my opinion ( and as you know, I like Tahitians ), but that mass has its drawbacks too.

 

Alloy is a material which can be used very effectively in yacht manufacture - however, as with any material, its all about how well its built, and how well the owner/maintainer understands the material. Get a surveyor who fully understands the build material before you purchase any boat and you should end up with a good one of the surveyor ticks all the boxes.

Link to post
Share on other sites
Wow that is a pretty negative list there allan,

Sorry, I didn't intend my post to be negative, I was trying to list the concerns because that is what RobT was really wanting to know after all and if what I have listed is the entire list of concerns, then actualy it is pretty good really. Being full of cold medication right at the mo, I am probably not thinking straight. But Doh!! yes ofcourse you cna use Zinc anodes. I don't know what I was thinking there. It's fresh water where you have to use Magnesium. Sorry about that.

There is a reason that almost all newer workboats are alloy - its a very durable, tough material for a boat to be made of, with the major advantage of it being very light.

One of the major reasons we see alloy boats today and we are of course talking the smaller trailer boats, is that every engineer and his dog can turn one out easily without any special gear other than what they have. Totaly unlike hulls biult in Glass. Especially in the last few years, mny engineering firms have been extremely quite and so many have decided why not biuld a boat. But just like any boat design, Alloy is no expception in regards to the critical need to get the Hull design right, or you end up with a Pig in Water, which many of the Powerboat hulls around are, expept for a few very well designed exceptions.

But as said already we are not seeing many yachts biult in Alloy and there are several reasons for that. In a larger complicated design like a yacht, they are not all that cheap to build for one. Right down to the time taken in getting the paint finish perfect, or end up with a mess several years down the track.

But I do hold on to my comments about temperature and noise, compared to any other material including steel. But that's just my opinion.

Link to post
Share on other sites

One of the major reasons we see alloy boats today and we are of course talking the smaller trailer boats, is that every engineer and his dog can turn one out easily without any special

gear other than what they have.

 

I think that the main reason a lot of trailered boats are alloy is purely weight - a 26' alloy boat might weigh in at a full tonne less than a 26' glass boat. The glass boat will be a challenge for most to tow ( need a 3.5T towing capacity vehicle, and even then, you really need powered brakes etc ) where as a 26' alloy boat is able to be towed by your average 6cyl aussie tank, your average 4WD or ute, etc. Also, you probably can get away with a 175HP motor on the alloy boat as opposed to a 250 - 300 on the grp boat.

 

BUT - your comments about noise and temp are very relevant on trailered boats, very much so. Not exactly a lot of insulation in those puppies - they are cold in the winter and not that pleasant of a place to be sitting in holding a bit of fibreglass with some nylon on it - for some reason mine never really has much more than a bit of lead on the end of it, not a large chunk of protein thrashing about trying not to be my dinner. But once you get into larger, moored boats, the scene changes quite a bit in my experience, specially with the newer launches built in alloy - they are designed to be comfortable, pleasant things to be in. Much like the GRP ones. Another benefit of alloy on this type of craft is that if you smack a sinker into the side, it wont chip a gel coat. Or, if your like me, you drop a chain on the deck of a 3 week old Tristram 781........ opps :D

 

But as said already we are not seeing many yachts biult in Alloy and there are several reasons for that. In a larger complicated design like a yacht, they are not all that cheap to build for one. Right down to the time taken in getting the paint finish perfect, or end up with a mess several years down the track.

But I do hold on to my comments about temperature and noise, compared to any other material including steel. But that's just my opinion.

 

I think that of the mass produced boats, you would be on the money in your comments about there not being a lot built in alloy. I suspect that there are more alloy boats on the water than you would expect. I know that I have been on a few yachts which you would not know were alloy till you look closely - in other words, inspect, once your on them. Even standing on one of them, I did not notice that it was alloy untill I looked closely at it. Teak decking and well finished paint really did make it look to be glass of some sort ( GOP, Trip diag glassed, GRP, etc.. ) That boat was one of the quietest when under way through a moderate chop that I have been in, it did not bobble around at all ( was an Allan Mummery design I believe ) and it was also not at all cold inside, even though it was mid winter at Riverton. On deck it was hellishly cold, though! Even sleeping on it at Stewdog you hardly noticed the slap of the waves.

Link to post
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...