Rib Transom Specs

[Bigplumbs]

If a new rib transom is rated to 75 hp which would be a 4 stroke probably weighing 150 kg.

If you wanted to go 2 stroke would you be happy to install say a 90 hp which weighs less than 150 kg.

I know a transom spec is about power and weight but would you think 15 hp over would be an issue.

I know it might have an issue with insurance

 

[[165042]]

It's always a HP rating regardless of weight (there's probably a max weight too). The simplest thing is to speak to the manufacturer but I suspect you'll struggle to get insured if you overate the CE plate it's certified for.

 

[Rappey]

It's always a HP rating regardless of weight (

Not so sure as honda 90 is only 20kg lighter than a yamaha 200 2 stroke of the same era.

 

[[165042]]

Sorry but what relevance does that have? Like I said you have a max weight and a max HP rating. You can't fit an engine that exceeds either one and still maintain CE rating.

 

[Boathook]

I suspect that the transom will take the power but how will the rib behave when you give it full throttle and as you mention the insurance.

Years ago I was chatting to a person on the Avon stand at a boatshow about an Avon rib that I had. It was rated at 15hp but the guy said they tested it with a 30hp. The boat took the power but they had to be careful not to tip it !

 

[Bigplumbs]

Sorry but what relevance does that have? Like I said you have a max weight and a max HP rating. You can't fit an engine that exceeds either one and still maintain CE rating.

I think you are missing the point. If you read my original post. I am aware of the possible insurance situation. This is not what this thread is about or indeed CE rating

 

[Momac]

The power of the engine causes a bending moment on the transom due to the power at the prop x the lever arm to the fixing to the transom.
Too much power could cause instability or structural failure,
So it would be wise not to exceed the 75hp.
But why not try the 90hp as is only 20% over the recommended maximum. What could possibly go wrong?

 

[SC35]

The manufacturer will have tested the boat with engines at the rated hp in the conditions it's expected to be used in.
Like a car, you can exceed those limits by tuning / increasing engine power, and you are "on your own".
Many people have done this, especially with tenders on this forum, and very few people have died doing it.

But ... if your transom is a fibreglass thing that is part of the hull and cracks appear ... you are on your own.
If the transom starts to un-glue itself from the tubes ... you are on your own.
Insurance claims could well be an issue if you have exceeded the plated HP ... you could be on your own.

On the other hand, if you only use the extra power fed in smoothly in flat conditions and you don't crash and the engine weight is about the same, you will be motoring past the slower boats .. in a category of your own

Personally, I would go for max plated HP and no more.

 

[[165042]]

I think you are missing the point. If you read my original post. I am aware of the possible insurance situation. This is not what this thread is about or indeed CE rating

Then what is it about? A CE rating is granted based on the design specification by the builder but obviously you know best so carry on.

 

[Rappey]

Sorry but what relevance does that have

None at all. Im not sure what i was thinking when i posted that.

 

[Boathook]

Then what is it about? A CE rating is granted based on the design specification by the builder but obviously you know best so carry on.

Likely problems to the transom (and dinghy handling) caused by putting a bigger than recommended engine on the transom.
My boat and one of the dinghies pre-dates CE so it is common sense for me.

Looking at some of the warnings written in the manuals nowadays, common sense seems to be in short supply !

 

[ylop]

Depends what your questions is…

Would I go out of my way to put a 90 on 75 transom- no that would be stupid.

If I had a spare 90 kicking around would I put it on the 75 transom - maybe but with some a big caveat that limiting the throttle (either mechanically or with operator intelligence) and fully knowing that if I had an accident that was not my fault and possibly had nothing to do with engine power that everyone (not just insurers), but MAIB, MCA maybe police would be saying I was wrong. And knowing that I’d struggle to sell it like that.

The reason for the 75Hp limit may be nothing to do with the mechanical strength of the transom, but the handling of the boat in its intended use setting. I’d look to other people with the same boat running 75Hp and see how close to the limit it seems. If it’s some novel or obscure boat either you are close enough to the builder to have the discussion direct or they have no idea and even 75Hp/150kg may be dodgy!

 

[SC35]

It's also worth pointing out that most standard RIB and engine packages have an engine that is one step down from the plated maximum.
e.g. plate says 150hp, standard package might be a 130hp or 140hp.

 

[Bigplumbs]

Then what is it about? A CE rating is granted based on the design specification by the builder but obviously you know best so carry on.

A CE rating is a certificate of compliance to assist buyers with a Purchase. Once you purchase such a vesel you can do as you wish. Also it might prove to be news to you but Insurance is also not a legal requirement for a boat in the UK. Now I know you and others will interpret that statement as me saying you don't need Insurance. Well that is not what I said but you will of course decide otherwise

 

[Bigplumbs]

Likely problems to the transom (and dinghy handling) caused by putting a bigger than recommended engine on the transom.
My boat and one of the dinghies pre-dates CE so it is common sense for me.

Looking at some of the warnings written in the manuals nowadays, common sense seems to be in short supply !

I was talking about a Rib. Where did dinghies get mentioned

 

[Bigplumbs]

It's also worth pointing out that most standard RIB and engine packages have an engine that is one step down from the plated maximum.
e.g. plate says 150hp, standard package might be a 130hp or 140hp.

Have you got a Rib

 

[dunedin]

A CE rating is a certificate of compliance to assist buyers with a Purchase. Once you purchase such a vesel you can do as you wish. Also it might prove to be news to you but Insurance is also not a legal requirement for a boat in the UK. Now I know you and others will interpret that statement as me saying you don't need Insurance. Well that is not what I said but you will of course decide otherwise

Third Party Insurance is often a requirement for many of the places where a RIB can be launched.
And anybody who uses a RIB with 70+ hp drive without at least third party insurance is taking a huge risk at best, probably antisocial and certainly unwise.

 

[Momac]

Insurance is also not a legal requirement for a boat in the UK

This depends where you want the boat to be in the water .
eg. On rivers and canals under Canal and River Trust or Environment Agency control a license is required and to obtain the license you need insurance.

 

[SC35]

Have you got a Rib

I have access to several - sailing club rescue RIBS that I helm a few times each year.
I don’t own a RIB … yet, but that could change.
Am I allowed to own more than one boat?

 

[stelican]

This depends where you want the boat to be in the water .
eg. On rivers and canals under Canal and River Trust or Environment Agency control a license is required and to obtain the license you need insurance.

Do you mean a Helmsman's license or vessel license ?
It may be difficult to obtain insurance without a recognised Helmsman's qualification.