Dinks with Aluminium Floors

[Relax]

I am contemplating a new dinghy at some point in the middle future (sail off into the sunset etc) - I only have two at the moment - an ancient Avon lilo and a tiny Plastimo which has had little use but is already rather 'sticky'.

Looking at a Honda or Lodestar - more heavy duty spec and probably in the 2.7 to 3.0 metre range. This is getting to the limit of what I think I could lift onto the foredeck.

Is it a good idea to get one with an aluminium floor? The idea strikes me as sensible in the long term - surely better able to take more abuse?

But is this borne out in practice? Does the floor stand up and does it wear the PVC where it is bearing on it?

If anyone has one long term I'd be interested to hear.

 

[noelex]

Aluminium dinghy are the only material that stands up to charter use in the coral areas of Australia. I have only had my aluminium floor dingy a short time so no personal long term report,
The aluminium floor is the toughest as well as the lightest option a good combination of features in a tender.

 

[Seajet]

Alloy does however have a finite lifespan, especially around salt water & air.

Probably as long as the inflatable though, if one looks after it with fresh water rinses as often as possible.

 

[Tranona]

By aluminium floor do you mean an aluminium hulled RIB or removable aluminium internal floor? The latter is not common as there is little advantage over wood slats, or now inflatable floors - and they are very heavy. Used to be popular on Zodiac sportsboats because you could get a very rigid floor for high speed work. Wasted on a tender, as now you can get inflatable keels on basic boats which allow good planing performance if you have the power.

 

[Relax]

Aluminium floor

From what I have seen briefly on our clubs 4m Honda safety boat its a much more rigid aluminium sectional floor - totally unlike slats and with an inflatable keel below to stop 'skidding' and give lift. The result appears to offer the best of several worlds and unlike a high pressure air floor has (I assume??) a pretty good resistance to scratches bumps etc.

The downside is weight - 3m Honwave is 54kg.

Just wondered if this was all a big advantage long term?

 

[noelex]

Alloy does however have a finite lifespan, especially around salt water & air.

Probably as long as the inflatable though, if one looks after it with fresh water rinses as often as possible.

Marine grade aluminium has an almost infinite life in salt water. It can corrode when in contact with other metals or if oxygen is prevented from reaching the surface, but this will not be a factor in the hull of a small RIB unless you do something very silly.
Fresh water rinses are not needed.

 

[Tranona]

From what I have seen briefly on our clubs 4m Honda safety boat its a much more rigid aluminium sectional floor - totally unlike slats and with an inflatable keel below to stop 'skidding' and give lift. The result appears to offer the best of several worlds and unlike a high pressure air floor has (I assume??) a pretty good resistance to scratches bumps etc.

The downside is weight - 3m Honwave is 54kg.

Just wondered if this was all a big advantage long term?

Can see the advantage on a bigger boat used as a rescue boat, where the performance and rigidity are important, but on a yacht tender you lose some of the advantages of an inflatable - light weight, ease of packing and assembling for very little gain. Inflatable floors and keels are popular because they improve performance and comfort with a smaller penalty on weight and portability.

If you have the means to handle the weight and the space to stow the inflated boat - plus you expect to hump heavy stuff such as dive gear in and out, then you might argue the case for an aluminium floor, but for normal tender use an inflatable floor is perfectly adequate.

 

[Talbot]

I have a 3m Honda with an aluminium floor, and it has a 6hp honda .

It is HEAVY

I plan to change this for a 3m Rib Eye ali rib at nearly half the weight

 

[KellysEye]

We have an aluminium floor dinghy, it is considerably lighter than a GRP dinghy. I don't know if you they are sold here but AB hold the yellow jersey for quality, it used to be Carib until they changed factory. We have the 9AL.

 

[Relax]

Rib Eye ribs

I have a 3m Honda with an aluminium floor, and it has a 6hp honda .

It is HEAVY

I plan to change this for a 3m Rib Eye ali rib at nearly half the weight

Look V tempting - but twice the price and obviously that wee bit harder to stow.

Just the jobby if you have davits or a huge foredeck.

(Thinks, might just fit though.............)

 

[Stu Jackson]

Too avoid damage to a high pressure air floor, install outdoor carpeting. Putting together a dinghy with floor gets tiresome very quickly compared to an air floor.

 

[KellysEye]

>Alloy does however have a finite lifespan, especially around salt water & air.

I don't think that's correct. If you look at the hulls of unpainted Aluminium hulls they have a white coating on them. This is Aluminiun Oxide which stops further corrosion.

 

[Seajet]

Alloy in salt water / air

>Alloy does however have a finite lifespan, especially around salt water & air.

I don't think that's correct. If you look at the hulls of unpainted Aluminium hulls they have a white coating on them. This is Aluminiun Oxide which stops further corrosion.

I'm afraid it is correct, alloy oxidisation only delays corrosion; I had a couple of 1977 vintage alloy backing pads turn to white powder then dust due to this.

Naval aircraft such as Sea Harriers etc use special alloys, particularly in the engine and vital bits, to try to offset the effects of salt air and spray.

Ovni's and similar are among my 'lottery win fantasy boats' as a relatively short term proposition, but when did you last see a healthy late 1970's built Sarum 28 ?!

 

[noelex]

I'm afraid it is correct, alloy oxidisation only delays corrosion; I had a couple of 1977 vintage alloy backing pads turn to white powder then dust due to this.

The backing pads are small piece of aluminium connected to other metals with no oxygen reaching the inside surface. This is poor use of aluminum. Its not the salt water, but a combination of galvanic and crevice corrosion will destroy the aluminum.
The floor of an aluminum RIB will not be subject to these problems.

Naval aircraft such as Sea Harriers etc use special alloys, particularly in the engine and vital bits, to try to offset the effects of salt air and spray.
!

Marine grade aloys are required in a salt water environment conventional aircraft aluminium would corrode due to the presence of copper. Its not surprising in areas of salt spray the aircraft required a different, marine, grade of aluminum

 

[Seajet]

The backing pads are small piece of aluminium connected to other metals with no oxygen reaching the inside surface. This is poor use of aluminum. Its not the salt water, but a combination of galvanic and crevice corrosion will destroy the aluminum.
The floor of an aluminum RIB will not be subject to these problems.


Marine grade aloys are required in a salt water environment conventional aircraft aluminium would corrode due to the presence of copper. Its not surprising in areas of salt spray the aircraft required a different, marine, grade of aluminum

I'm intrigued as to how you know the backing pads involved - and their installation - better than me, plenty of oxygen available for a start or I wouldn't be writing this !

They were in fact reasonably open to salt air, inside cockpit coamings ( although 2mm+ thick and originally coated with 'Duralac' zinc chromate paste).

Alloy masts etc get away with it as they are a different proposition, anodised from new.

Crevice corrosion is more of a worry with stainless steel, and I might avoid jumping into aged aluminium floored dinghies, particularly as with some users there are alligators, crocodiles or similar about !

BTW Magnesium was the worry re. Naval aircraft.

 

[noelex]

I'm intrigued as to how you know the backing pads involved - and their installation - better than me, plenty of oxygen available for a start or I wouldn't be writing this !

They were in fact reasonably open to salt air, inside cockpit coamings ( although 2mm+ thick and originally coated with 'Duralac' zinc chromate paste).

Alloy masts etc get away with it as they are a different proposition, anodised from new.

Crevice corrosion is more of a worry with stainless steel, and I might avoid jumping into aged aluminium floored dinghies, particularly as with some users there are alligators, crocodiles or similar about !

BTW Magnesium was the worry re. Naval aircraft.

The backing pads have a low concentration of oxygen on the inside face.

You would not be writing this is if you had to live at this oxygen level.

Stainless steel hardware is almost universally used to attach the cleat or winch etc to the aluminium backing plate. Often the attached hardware, the cleat or winch, is also stainless steel or another dissimilar metal
So there is a combination of galvanic and crevice corrosion attacking the aluminium. As there is a relatively small piece of alumium the attack can be rapid. It is fortunate that the backing plates survived 10 years.
Alumium backing plates are not a good idea it is a very poor use of the material. Their short life is due to galvanic and crevice corrosion.
Aluminium masts fare better because they are relatively large mass with only small amounts of dissimilar metal attached to them. Unfortunately the aluminium required for masts is not as corrosion resistant as is used on hulls, but with steps taken to isolate the dissimilar metals they can have a good life.
Hulls can be made of more corrosion resistant aluminiums and have a very small amount of dissimilar metals attached to them. With an RIB tender there is typically no other metal electrically attached to the hull.

 

[Seajet]

I am afraid my engineering training, qualifications and chiefly experience lead me to differ...I am familiar with dissimilar metal corrosion and masts

 

[Sarum 28]

Seajet wrote.

Ovni's and similar are among my 'lottery win fantasy boats' as a relatively short term proposition, but when did you last see a healthy late 1970's built Sarum 28 ?!

There are curently several Sarum 28 on the market.
And I am interested to buy one.
I visited in Portland last year a bilge keeler outside the water and noticed some brown typical iron corosion at the keel.
Propably the keel is made of iron. The junction will then be a point of galvanic corosion.

But your statement seems more general:
Is the Sarum known as a boat with general coroded aluminium hull material?
When I read that the builder Barco has a production line of aloy working boats, I valued that as a good reference.
But your statement seems to underline a bad reputation of the Sarum 28.
Thanks,

 

[Boathook]

Why not consider a second hand tinker foldaway. GRP floor and hypalon tubes. I would say new but Henshaws stopped production a couple of years ago due to economics.

 

[ytd]

aluminium dinghys and aluminium floored ribs are very common here in Aust. I have never known a the alu rib floor to corrode before the hypalon tubes disintergrate. Similarly alu dinghys (tinnies) are scrapped because the alu has worn away from dragging over coral or concrete ramps rather than corrosion. alu in dinghies lasts much longer than in masts and booms beause there are no stainless fittings attached to it. we have just scrapped a 12 year old rib because the hypalon is delaminating and leaking. the alu hull is fine wiyh only a small amount of corrosion on the transom near the outboard mounting point