Avon Spitfire 3.4M engine size

[martin33100]

Hi, I have just bought a really nice Avon Spitfire 3.4M SIB from one of my parents neighbours as it's just been sat on there drive for years and not been used, it's cleaned up really well.
It came with the trailer and 4hp Mercury but from previous experience I want to get a much larger motor.
Our old Honwave 3.8M had a nice late Yam 15 2 stroke but even that was under powered with 3-4 adults.

Our Avon is rated at 25hp and as most 20's and 25's are the same engine so same weight on the back I was thinking of just buying one of the last 25 2 strokes.
The other engine I have considered is the Tohatsu 18 2 stroke but they seem very rare to pick up used.

Any views will be greatly appreciated.

This is our new toy

[jeffstevens763@g]

stick a 25 on it and have fun

[martin33100]

Originally Posted by jeffstevens763@g

stick a 25 on it and have fun

I probably will, my old Jam 15 got lifted on and off our old SIB every trip out so at aprox 35kg it was very light.
I will probably keep the engine locked on this new SIB so I guess a slightly heavier engine shouldn't make much difference.
For reference something like a Tohatsu 2 stroke 9.9,15,18 is 41kg and there 25 is 51kg.

[jeffstevens763@g]

Originally Posted by martin33100

I probably will, my old Jam 15 got lifted on and off our old SIB every trip out so at aprox 35kg it was very light.
I will probably keep the engine locked on this new SIB so I guess a slightly heavier engine shouldn't make much difference.
For reference something like a Tohatsu 2 stroke 9.9,15,18 is 41kg and there 25 is 51kg.

To be honest I've never been a fan of lifting engines on and off they are the most awkward unbalanced bit of kit out there even in my youth when I was lifting heavey stuff down the mines I found outboards a pain in the butt. Your boats on a trailer launch where it's easy for you job done a 25 will do all you want. Nice boat too

[martin33100]

Originally Posted by jeffstevens763@g

To be honest I've never been a fan of lifting engines on and off they are the most awkward unbalanced bit of kit out there even in my youth when I was lifting heavey stuff down the mines I found outboards a pain in the butt. Your boats on a trailer launch where it's easy for you job done a 25 will do all you want. Nice boat too

It's just something to get my boys out on the River Hamble on, mum and dads neighbour only wanted £300 for the boat, trailer and Merc 4 so I quickly went up the cash point before he changed his mind.
We did have a nice Avon Adventure D560 with Merc 90 but that got sold when we had are first son.
I am sue we will get another RIB when our boys are bigger.

[jeffstevens763@g]

That's a Bargin bet usane bolt wouldn't have beat you to the cash point enjoy post some pics when you get her sorted.

[Stubber]

Cracking boat, I have an Avon 3.4 and yet to try a mercury 25 2stroke that I purchased months ago, the 15 mariner that I have is OK 2 up but struggles with 3 hefty guys in boat

[martin33100]

Originally Posted by Stubber

Cracking boat, I have an Avon 3.4 and yet to try a mercury 25 2stroke that I purchased months ago, the 15 mariner that I have is OK 2 up but struggles with 3 hefty guys in boat

That's exactly my concern, my old Honwave 3.8 was fine with 2 up on a Yam 15 but anymore and it would struggle also.
Our two boys are only 4 and 6 but growing fast so a 20/25 would probably future proof are needs especially if we ever get a bigger SIB.

[Stubber]

Yes definitely, but although you are comprising weight of engine, as said the 15 is portable to a degree where as a 25 isn't really, I have gone with trailing my Avon as setting up is a pain and it's heavy but will probably take engine off for towing but from van to boat is probably OK for me to lift hopefully, everything seems a compromise, weight, and size etc

[Roflhat]

The old mercury/mariner 25 is the same block as the 30hp, may as well get one of them

[jeffstevens763@g]

Originally Posted by martin33100

That's exactly my concern, my old Honwave 3.8 was fine with 2 up on a Yam 15 but anymore and it would struggle also.
Our two boys are only 4 and 6 but growing fast so a 20/25 would probably future proof are needs especially if we ever get a bigger SIB.

the problem is the 15 will always be at its limit where as the 25 will have more power than you need and respond better in the rough.
i ve never trailed a boat without the engine fitted if its set up properly and supported you will have no problems and your back and engine won't suffer.

[martin33100]

I have just enquired about a nice 20 mariner 4 stroke, not much heavier at 53kg but from memory they do the weights with no oils.
I do like the get up and go with the 2 strokes though.

[martin33100]

Originally Posted by Roflhat

The old mercury/mariner 25 is the same block as the 30hp, may as well get one of them

Are you talking really old as I thought the 2 stroke 20/25 had the same block.

[Roflhat]

Originally Posted by martin33100

Are you talking really old as I thought the 2 stroke 20/25 had the same block.

Yeh the 80's/90's ones the 25/30 is the same block. On the newer, around 2006 Mercury/Mariner/Tohatsu the 25 and 30 share a block too, the 2 cylinder versions

[Stubber]

In my way of thinking a good 2 stroke is the way to go as less to go wrong and Servicing is simple if you do it yourself and a hell of a lot cheaper and a little lighter, although fuel use is more and everything 4 stroke is getting lighter little by little but all the complications of 4 stoke for a portable engine makes me go for 2 stroke at the moment

[pagick]

I had a 1983 version of your boat. It had a 30 hp 2 stroke. Back then the 30 weighed 115 lbs (us) 4 strokes have less hole shot.
Real fun. We could wakeboard with only driver in the boat.
2 still fast, 3 so so 5 it was a displacement Hull.
Changing the prop 2-3 pitch down makes it better but top speed drops. And you have to keep an eye on revs