polyester vs aluminium RIB

[rigpigpaul]

Hi All, I am looking to buy a 3.1m rib. I have been looking on the Plastimo website. They have polyester hulls and aluminium hulls. The weights are very similar. What are the pros and cons of these hulls? Corrosion, grounding on the beach, easily marked? Thanks in anticipation.
RPP.

 

[Bobc]

I think the polyester ones are heavier. I have a 3.1m polyester Plastimo and have found it a good RIB.

 

[TQA]

There have been a number of early failures on ali ribs in the cruising community.

Some may be linked to electrickly 'hot' marinas.

But others are somewhat mystifying as it appears there is some galvanic reaction between the ali and the fabric leading to rapid ' bubbly ' corrosion.

The above has resulted in the dinghies being scrapped at less than 3 years of age. In some cases the manufacturers have offered some assistance with a replacement.

 

[t21]

Aluminium dinks are supposedly lighter per unit length than GRP, but they are so "tippy" I wouldn't consider them again - they shift about quickly as you move around them, and they're also super-noisy - a tin can belting along at 20knots or whatever.

My best combination is found in the caribbean - a Carib 12 (slighly better deeper-vee hulls than AB) and Yamaha 15hp 2-stroke.

 

[vyv_cox]

But others are somewhat mystifying as it appears there is some galvanic reaction between the ali and the fabric leading to rapid ' bubbly ' corrosion.

Incredible. No matter what you think you know about corrosion it will still catch you out! I can only assume that the elastomer being used is filled with some conducting material. Carbon is widely used but I doubt it is graphite, so probably an insulator. Metal powder? Never heard of it in this application. Any metal strips used to fasten hull to tubes?

 

[geem]

Incredible. No matter what you think you know about corrosion it will still catch you out! I can only assume that the elastomer being used is filled with some conducting material. Carbon is widely used but I doubt it is graphite, so probably an insulator. Metal powder? Never heard of it in this application. Any metal strips used to fasten hull to tubes?

I know of one AB rib that had extensive corrosion problems. It was only two years old and had to be scrapped. I didnt think it was a problem of a reaction between the glue and aluminium. The aluminium corroded so badly that the rib leaked at the hyperlon/ali interface. AB refused to accept a warranty claim. I wondered if the corrosion was an issue with its connection to a faulty outboard?

 

[vyv_cox]

I know of one AB rib that had extensive corrosion problems. It was only two years old and had to be scrapped. I didnt think it was a problem of a reaction between the glue and aluminium. The aluminium corroded so badly that the rib leaked at the hyperlon/ali interface. AB refused to accept a warranty claim. I wondered if the corrosion was an issue with its connection to a faulty outboard?

It would be interesting to know what grade of aluminium was used in construction. 1xxx is widely available as sheet but has the worst corrosion resistance. Not sure if the grades with best corrosion resistance are produced as sheet.

 

[TQA]

It looks like it could be a glue related problem.

One of the dinks was corroded next to the joint between the fabric and the floor. Not yet leaking but about 75 % corroded through at 2 years of age or less. That dink did spend a fair amount of it's time in Caribbean marinas. There are complaints of similar problems.

But I have also seen the other problem where the floor ali seems fine but the glue joint is failing between the floor and the fabric with definite seepage. The dink was about 18 months old. Looking closely at the joint it was as if the ali was bubbling but the dink owner did not want any body poking at it as there was an ongoing warranty discussion.

 

[RichardS]

We bought a superlight Highfield alloy dinghy because they are much lighter than the GRP versions. It might not always be the case depending upon the construction of the dinghy but our is basically a single skin with a few internal bracings and no internal skin structure. It is very light and is 5 years old now with no corrosion and I wouldn't say that it is any noisier than the GRP versions but with only a 2.5 outboard we're not going very fast. However, it is certainly a lot more "tippy" as the lack of weight means that it sits high in the water.

Richard

 

[geem]

We bought a superlight Highfield alloy dinghy because they are much lighter than the GRP versions. It might not always be the case depending upon the construction of the dinghy but our is basically a single skin with a few internal bracings and no internal skin structure. It is very light and is 5 years old now with no corrosion and I wouldn't say that it is any noisier than the GRP versions but with only a 2.5 outboard we're not going very fast. However, it is certainly a lot more "tippy" as the lack of weight means that it sits high in the water.

Richard

We used to have a Caribe 9ft Light. These are GRP. It weighed 54kg. It was super stable but relatively heavy for its size compared to the equivelent sized aluminium rib. It went very well with our 9.8hp. Our friend has a smaller (i think 8ft ) superlight AB aluminium rib and with the same engine it is a poor performer. Its super tippy but with two people in it takes and age to get on the plane even with a planing plate on the engine. Its not supposed to have a 9.8hp fitted. I think the plate on the hull says 6hp.
Put any weight in it and forget planing. I think one of the issue with single skin aluminium ribs is the limits of hull design given what can be achieved pressing an aluminium shape. The GRP hulls in my experience have better hull shapes as they are easier to make.
We now have a hard nesting dinghy instead of the rib.

 

[Jeva]

We bought an aluminium dinghy 8-9 years ago. Never had a problem. Would never go back to plastic again.

 

[geem]

We bought an aluminium dinghy 8-9 years ago. Never had a problem. Would never go back to plastic again.

It depends how you use it I think. Permanent liveaboard friends on a couple of boats we know are unhappy with their aluminium dinks due to corrosion issues. One has Highfield the other AB. One has now gone for a hard dinghy. Every day use certainly takes it toll on ribs

 

[Bouba]

It depends how you use it I think. Permanent liveaboard friends on a couple of boats we know are unhappy with their aluminium dinks due to corrosion issues. One has Highfield the other AB. One has now gone for a hard dinghy. Every day use certainly takes it toll on ribs

I have an small aluminum rib, if the hull gets marked I touch it up, I would do the same with a grp hull. Are people saying they rot even with maintenance?

 

[Kelpie]

I have an small aluminum rib, if the hull gets marked I touch it up, I would do the same with a grp hull. Are people saying they rot even with maintenance?

Touch it up with what?
I thought one of the advantages of al was that it didn't need to be painted.

 

[Bouba]

Touch it up with what?
I thought one of the advantages of al was that it didn't need to be painted.

Paint.
Anything made of anything needs maintenance. I’ve heard wooden boat owners say that grp boats don’t need maintenance but it’s not true. Alu ribs get scratched and obviously if the factory coating wasn’t applied perfectly then it’s possible that it will bubble up under the paint. I will be honest and say that I chose my Highfield 2.6m rib because it’s beam was narrow enough to fit on my boat deck, the aluminum was not a deciding factor. It’s not used a huge amount but it is dragged up on the beach often (the Highfield does have a rubber keel protecting strip, which is nice) and it’s very often full of water from rain and splashes. But it’s been no problem. Just to note the Highfield is coated in a white enamel paint of some sort but there are bare aluminum craft (including large yachts) which is a different thing.

 

[Talbot]

I have a RibEye ali boat. It is epoxy powder coated, but also has a plastic skid strip up the keel. Mine is 6 years old and does exactly what I want it to! I managed to find a Tohatsu 9.8 2 stroke which is a great match. The two together weigh less than the previous Honwave ali decked inflatable on its own.

 

[Kelpie]

I'm surprised to hear that RIBs are coated/painted. Ovnis seem happy enough with a bare hull. I use a 30yr old bare aluminium workboat every day, and it lives in saltwater 12 months of the year, running up rocky beaches etc, without so much as a lick of antifoul on it.
The only thing I can think of is that these larger boats have thicker hull plating, so perhaps it is a totally different grade of aluminium. Do RIBs need to use a stiffer grade of material, which is more susceptible to corrosion?

 

[geem]

Paint.
Anything made of anything needs maintenance. I’ve heard wooden boat owners say that grp boats don’t need maintenance but it’s not true. Alu ribs get scratched and obviously if the factory coating wasn’t applied perfectly then it’s possible that it will bubble up under the paint. I will be honest and say that I chose my Highfield 2.6m rib because it’s beam was narrow enough to fit on my boat deck, the aluminum was not a deciding factor. It’s not used a huge amount but it is dragged up on the beach often (the Highfield does have a rubber keel protecting strip, which is nice) and it’s very often full of water from rain and splashes. But it’s been no problem. Just to note the Highfield is coated in a white enamel paint of some sort but there are bare aluminum craft (including large yachts) which is a different thing.

The ali ribs Made by AB are unpainted. They still corrode. I guess its down to personal preference but I preferred our GRP rib over ali. We now have a hard dink which is of course GRP

 

[KellysEye]

I switched from a polyester dinghy to a AB Lamina 9AL dinghy the difference in weight was demonstrated by - with the 5HP engine the polyester dinghy wouldn't surf the aluminium one did. We didn't have a corrosion problem.

 

[geem]

I switched from a polyester dinghy to a AB Lamina 9AL dinghy the difference in weight was demonstrated by - with the 5HP engine the polyester dinghy wouldn't surf the aluminium one did. We didn't have a corrosion problem.

You might not of done but many do. I have seen some pretty corroded ali ribs out here in the Caribbean. Ribs here get a hard life. Lots of local dinghy docks are rough concrete or rusty steel. Tubs get scratched even if they are painted. Once you have a scratch on painted ali its hard to get paint to stick again. You need a paint pretreatment like Alacrom prior to a good epoxy undercoat then topcoat. I dont know anybody that does this so tubs just get worse as the corrosion gets under the paint