30hp outboard on a sib marked as a 25hp max?

[Stevenmb]

I'm just curious but I recently brought a 30hp outboard. I'm looking for a sib but a lot of the newer sib's are marked up to 25hp. Surely if 25 hp engines and 30hp are effectively the same there should be no problems that arise from it while at sea? Also curious if I put it on a sib marked as a 20hp max on transom. My budget is limited. I currently have it ready to go on my avon sib which is rated up to 40hp but the inflatable keel has given up with multiple leaks in hard the patch areas .
Any advice would be great
Cheers Steve

[Ribochet]

Originally Posted by Stevenmb

Surely if 25 hp engines and 30hp are effectively the same there should be no problems that arise from it while at sea?

Hi Steve - welcome to RIBnet

Maybe you could clarify what you mean by "effectively the same"

For example apart from the 20% difference in power and subsequent speed - a Yamaha F25LA weighs 81kg where as a Yamaha F30LA weighs 97kg - that is 16 kgs (that also is nearly 20%) all of which will make a huge difference on the back of a SIB.

[Max...]

Those older Avon SIB's were much higher rated in terms of HP than more recent PVC types.

[Stevenmb]

From reading other previous post I come to understand that 25and 30hp engines are you same. I own an old Suzuki dt300 which I brought recently at a boat jumble sale in plymouth at a bargain price of £140 and it runs perfectly, however it feels exactly the same weight as a 15hp mariner 2 stroke I used to have on my sib. So if a sib rated 20hp max can can the 15hp surely it can take the 30hp without any issues?

[Bern Hanreck]

Steve , you may just want to run the idea past your insurers before you go ahead ?

[Max...]

Originally Posted by Stevenmb

From reading other previous post I come to understand that 25and 30hp engines are you same. I own an old Suzuki dt300 which I brought recently at a boat jumble sale in plymouth at a bargain price of £140 and it runs perfectly, however it feels exactly the same weight as a 15hp mariner 2 stroke I used to have on my sib. So if a sib rated 20hp max can can the 15hp surely it can take the 30hp without any issues?

Why? The ratings are there for a reason - why should a SIB rated to 20hp be fine with a 30??!

There is no way a 25 or 30 weighs the same as a 15. The Mariner 15 2 stroke is about the lightest 15 out there at 34kg.

[Landlockedpirate]

I think I now where you are coming from. i.e. A 1990 Yamaha 2 stroke 25hp Origin is the same engine as a 1990 2 stroke 30hp Yamaha, just with more power.

Lots of people over engine boats, but you need to make a considered judgement on what is safe.

First thing would be to check with your insurance, I dont just mean insure the boat with the bigger engine on the policy. You should tell them you want to use an engine that is Xhp over rated for the boat and get it in writing that they will cover you if it all goes wrong.

Consider how much you are going to over rate, take into account weight and power of the engine. In a few cases (the Yam above) the 25 is the same as the 30 but it most cases its a world of difference with the 25hp being 2 cylinder and the 30hp being 3 cylinder and 30-50% heavier.

What is the condition of the boat ? A 20 year old sib designed for a max 25hp 2stroke wont last long with a 30hp 4 stroke on it, it will either rip the transom support pads or shred the glue very quickly.

I respect that you have asked the question, but the fact that you have needed to ask tells me you shouldnt do it.

There are a few sibs that will take a 30hp, Honwave T40, Zodiac Futura, Xpro Commando etc, you just need to look for them. Or sell the 30hp for a profit and find a smaller one.

[steco1958]

If you put a larger engine on the rear of a rib, or sib that it is rated for, you instantly give any insurance the excuse they require not to pay out if anything goes wrong.

If that was the case, and it was me you injured, I would come after you with a very big solicitor and take everything you owned, possibly even your freedom. limits and rating are there for a reason !!

[henryfreston]

with two stroke e.g. mercury, tohatsu amd mariner the 30hp and 25hp are the same engine, but the 25hp has a gasket restricting the air flow.

So a 30hp on a 25hp rated sib should be fine, can't see anything wrong if they are the same weight. The only issue you have is insurance unless you change the stickers to 25hp?

Henry

[rik_elliott]

Changing the stickers would leave you criminally culpable for insurance fraud should the worst happen.

Find a friendly insurer that will accept you overpowering the boat, or change the boat/engine to something more suitable.

[stray]

I'm sure all Sibs can take bigger engines than the maximum stated on the Transom. But the maximum stated is there so the SIB can operate within its safe limits. Exceeding the maximum stated engine size could push the SIB beyond safe operation.

If you decide to use a bigger than stated outboard, then I'd recommend trying to get specialist insurance cover, because a claim on normal cover would be thrown out because you breached it's terms and conditions.

[Roflhat]

Just use a 25hp and remove the restrictor, will give you 30hp (depending on what kind of engine of course).
If it were me I'd slap a 50hp on the back.

If possible you may want to strengthen your transom to take the extra power as well

[Stevenmb]

Thank you for your replies, as a novice to boating ( been out couple times with my mates) I presumed that all 30hp engines are the 25hp engine just without them being restricted. The engine I have is a 2 stroke 2 cylinder ( 2 spark plugs ( sticker says one is16hp and other is 14hp) ). I also I understood that the transom can often hold more weight etc however they lower it as a way to cover their self from liability if a transom was to fail. My example of this is my boat is roughly 3-4 metres which states it holds a 40ph (2 stroke back then) however the newer boats which are the same size are rated to a max of 30hp( ie the hon waves ) however most of the avon sports only go up to 25hp. So being the same boat pretty my question is surely it wouldn't effect the boat at all as it's only 5 hp more then it states? I realise in terms insurance it might be an issue however I would have asked that once someone gave me there experienced knowledge about the issues it might cause. I'm sure plenty of people have put a bigger engine on a boat then stated. I obviously I wouldn't put a 50hp on a transom maxed at 25hp but surely a 30hp on a 25 wouldn't be that bad?

[69cmw]

Originally Posted by steco1958

If you put a larger engine on the rear of a rib, or sib that it is rated for, you instantly give any insurance the excuse they require not to pay out if anything goes wrong.

If that was the case, and it was me you injured, I would come after you with a very big solicitor and take everything you owned, possibly even your freedom. limits and rating are there for a reason !!

If your insurance company insure a bigger engine, what's the problem?

[henryfreston]

Originally Posted by Stevenmb

Thank you for your replies, as a novice to boating ( been out couple times with my mates) I presumed that all 30hp engines are the 25hp engine just without them being restricted. The engine I have is a 2 stroke 2 cylinder ( 2 spark plugs ( sticker says one is16hp and other is 14hp) ). I also I understood that the transom can often hold more weight etc however they lower it as a way to cover their self from liability if a transom was to fail. My example of this is my boat is roughly 3-4 metres which states it holds a 40ph (2 stroke back then) however the newer boats which are the same size are rated to a max of 30hp( ie the hon waves ) however most of the avon sports only go up to 25hp. So being the same boat pretty my question is surely it wouldn't effect the boat at all as it's only 5 hp more then it states? I realise in terms insurance it might be an issue however I would have asked that once someone gave me there experienced knowledge about the issues it might cause. I'm sure plenty of people have put a bigger engine on a boat then stated. I obviously I wouldn't put a 50hp on a transom maxed at 25hp but surely a 30hp on a 25 wouldn't be that bad?

There is no performance problems using a 30hp, its just if the insurance company will play ball.

[Landlockedpirate]

Originally Posted by 69cmw

If your insurance company insure a bigger engine, what's the problem?

Because when you take out the insuance most companies dont do any checks i.e. You could insure a slat floor 2.4m Zodiac with a 40hp engine on it no problem.

But in the small print it will say the engine must be suitable for the boat, so when you have an accident then they will do the checks and you will be up a creek........

[Seaflyer02]

If you insist on fitting an engine of higher rated power output than the boat manufacturers Maximum rated horsepower then ask yourself this: - if anyone gets injured from your boat/engine, what defence will you give in court for overpowering it because seeing how the legal system works I for one would not put myself in your shoes. This is before we even go down the insurance route as previously mentioned.

Just one more thought, I have seen on this thread about reference to engine weight on the transom, that is only one consideration. Think of the power of the outboard trying to twist your motor/transom from the back of your boat. The manufacturers have calculated how much force can be applied to the transom SAFELY.
I have seen a 25HP clamped to a SIB (not bolted through) when put through a tight turn twist itself off the transom, the only things stopping it become a liberated anchor was the Teleflex steering and the remote cables - Oh and the guy clinging on to it for his life!

[Landlockedpirate]

Originally Posted by Stevenmb

Thank you for your replies, as a novice to boating ( been out couple times with my mates) I presumed that all 30hp engines are the 25hp engine just without them being restricted. The engine I have is a 2 stroke 2 cylinder ( 2 spark plugs ( sticker says one is16hp and other is 14hp) ). I also I understood that the transom can often hold more weight etc however they lower it as a way to cover their self from liability if a transom was to fail. My example of this is my boat is roughly 3-4 metres which states it holds a 40ph (2 stroke back then) however the newer boats which are the same size are rated to a max of 30hp( ie the hon waves ) however most of the avon sports only go up to 25hp. So being the same boat pretty my question is surely it wouldn't effect the boat at all as it's only 5 hp more then it states? I realise in terms insurance it might be an issue however I would have asked that once someone gave me there experienced knowledge about the issues it might cause. I'm sure plenty of people have put a bigger engine on a boat then stated. I obviously I wouldn't put a 50hp on a transom maxed at 25hp but surely a 30hp on a 25 wouldn't be that bad?

In a lot of cases it wont be a problem at all, but you need to have the experience to understand that. Older boats were much, much heavier than modern PVC sibs and so sticking a 40hp on an old Avon with an over engineered transom that weighed the same as the Forth Bridge wasnt a problem.

I will try to give you an example. The Zodiac Futura Mk2C Fastroller is rated to 25hp. With 1 person on board and a 25 the boat becomes a rocket ship, right on the edge of safe performance for a sib. It even starts to chine walk on the speed tubes if you get just the right amount of popple on the water. Stick a 30hp on it and it can go wrong very quickly, throwing the helm or even flipping the boat.

But at the other end of the spectrum, putting a same weight 25hp motor (instead of the stated 20hp max) on a fully loaded new Honwave T35 wouldnt be an issue (insurance accepted).

My dad over engined all of his speed boats in the 70's and 80's, mainly because we needed the performance for barefooting, but back then insurance was easy and 'Where there's blame there's a claim' firms didnt exist. These days its just not worth the risk.

Of course you could just ignore the advice and do it anyway .......

Inflatable Boats with 25hp flips in Ontario Lake - YouTube

[simon23]

Has anyone ever overpowered a boat,been honest with the insurance company and got cover that will pay out?

[69cmw]

Yes, twice over the last 16 years, both times they paid out satisfactorily and that was for 2 theft claims.