Wanting to upgrade motor size

[Seahorse]

I seriously thinking upsizing motor from 50 to 70.

My boat is says max 50 hp, which I have 50 yammy 4 str
I know Kondo did his upgrade but had to have his boat re certified.

The 70 is only 4 kg heavier. Max weight is 120 kg. the 50 is 117 kg and the 70 is 120 kg.

I have written 2 emails to seajay telling them what I want to do and as yet not received a reply.
You ring the agents and they just quote the book specs.

If u are within you weight limits then what's the problem?

I went to northside marine today and asked them about their motor limits and I was told that it's not a weight thing, it's an all over safety thing.
I think that's BS.
Do u think they only build boats to a motor size or do they think they might fall apart if you put a slightly bigger hp on the back but keep within the weight limits. The difference in weight is only. Good breakfast.

I would have thought that it would be better driving a boat at 75 % of its capacity to flat out for the smaller motor would be a better thing?

Well I will just have to wait and see.

What does amaze me is the response u get from boat sales staff. I called into northside marine today and asked about cc and jut wanted to talk me into their top range, I sent email to stones corn marine 2 days ago about upgrading my boat and asked for quotes. As yet no reply.
Went to yammy place at narangba, bloke their wasn't really interested.

Well I would say those 3 are off my list if I decide to buy new boat.

That's my beef today.


Cheers
Greg

[thylacene]

From my limited understanding, max transom weight is calculated based on hull weight and displacement.

Max HP is determined by transom design, material and bracing, or in lay mans terms, how much "push" it is designed for, if you consider the additional stress exerted by having the energy at the prop using the length of the leg as a lever (like putting a piece of pipe on a socket bar), the force applied to the transom is considerable.

The third consideration is that without re-rating you expose yourself to risk of fines and inability to claim on insurance, even if you are "in the right".

The increase from 50hp to 70hp represents a 40% increase, you might need an engineers certificate.

[bf90]

Mate years ago I had a bluefin 3.9 with a 25 johnno all new. The boat was rated to 30 hp. After a year I sold the 25 and strapped a 40 johnno on the back, only 10 hp over rated :) within 6 months the boat was totally rooted!! The hull had cracked over 80 times in different places and I ended up with a 50 mm hook in the bottom of the hull :) yep I broke its back :) and that was just with 10 hp over the max rating cheers brad

[Moonlighter]

The short answer (haha) is that there is a way to calculate the max power for a hull, and the formula is specified in the Australian Standard AS1799. Boats have to have the mx hp stated on the ABP, and it has to be worked out in accordance wit that Standard, or another accepted international one, but they all produce much the same result.

It goes like this:

Factor = overall boat length x boat width at transom at waterline.

Then:

16 x Factor - 67, Then multiply by 1.32 = max hp.

So, as an example

A 6 m boat with a 2.45 m beam would work out like this :
16 x 13.2 - 67 = 142 x 1.32 = 187 hp.

Then, the manufacturer or certifier (ie naval architect) has to do some specified on water tests and the boat must pass them, otherwise the max rating must be reduced until it does pass. Look up the standard and you will see the tests required, they are pretty rigorous.

Go and measure your boat and apply the formula and see what you get.

When you put a motor on that is over the boats limit stated by the manufacturer, YOU are now assuming all responsibility for the safe performance of that boat.

Are you prepared to take on that risk, and all the potential consequences that go with it?

That is what you are asking the dealers to do. Does that help you understand why they don't want to know anything about what you are proposing?

Hope this helps you to understand.

Cheers

ML

[WalrusLike]

There's some bloke with a lever bar trying to break my transom.

It's engineered to withstand his strength on the lever. All is well.

Now some other 40% stronger bloke wants a go....

[matt fraser]

From my experience, alluminium boat manufacturers won't re-rate their hulls, they are very rigid on it.

I tried a few years ago to get one of them to allow a 50hp rated hull to take a 60hp. Didn't happen.

You might have to go for a new boat, and find a tinny (or plate) manufacturer that is willing to work with you.

Shame about the service you've received, Emails probably aren't the way to go, but I thought boat salesmen would be going the extra mile atm.

Cheers,

Matt

[Kondo 1]

Gday Greg,

Seajay wont touch the upgrade full stop - I spoke to them about it a few times and they wouldn't have a bar of it.

If you want to legally upgrade the motor you need it re-certified by a marine surveyor, not expensive and no work required on my hull at all...

If you want his details PM me.

You wont know yourself the difference is that great. The 70 is a great match - though be aware there is quite a bit more torque transfered to your arm, good trimming does usually counteract most of that though.

[Seahorse]

Hi Pete.
I will send you pm.

[Si]

Do you want the extra horse power for more top end speed? I think no matter what motor you have you will always want more speed. I used to have a 115hp merc and extra speed was often wished even though i was going quite fast already. I think it's a perception thing. I'm happy if my 'boat' gets on the plane with three up and a bit of gear. Im not looking to break records.

I personally think it would be easier if you sold your boat to me for about 3k and bought a fibreglass CC that gives you the ride comfort and speed you desire then to get approval on upgrading motor and changing existing boat from Tiller to CC.

[Seahorse]

Si.
You are a funny fellow. But if you wanta pay deposit of $3k that's fine.