what outboard for 3.3m sib

SteveBoyle · 16 June 2023, 17:33

Hi, I'm new to boating so have a question about what outboard to get.
I have bought a tobin sports 3.3m sib with air keel. It's rated to 15hp.
Would a 10hp 2 stroke (fairly old age I think, but in good nick), or a mid 2000's 6hp 4 stroke be better? Will have 2 adults and a soon to be teenager on board.

Mostly be used on freshwater but want a bit of fun aswell.
Will also be lifting on/off on my own.

Any advice gratefully recieved.

Matt73 · 17 June 2023, 16:37

The 10hp would be much better and would do the job i used one on a t38 for a while with 2 adults and 2 kids. A 15hp 2 stroke would be my choice if you can find a good one as they are usually around the same weight as the 10.

Fenlander · 17 June 2023, 18:36

Hi Steve and welcome to the forum. We have frequently been 2 adults and one slim teen girl in SIBs from 3.4-3.8m. A 6hp will not move you at all well if at sea. A 10hp is about the minimum to plane this load, it's what we have now on a light air floor 3.8 (43kgs) and achieves 15kts.

Having said that if your freshwater use is just the river or restricted lake then the speed limit will easily be reached by a 6hp... even a 4hp.

Note Matt's comment re the weight. Many of the 2-stroke 10hp motors were just detuned 15hp models, the only true light 10hp is the Tohatsu 9.8 2-stroke.

Steve509926 · 17 June 2023, 22:31

Hi Steve, welcome to the forum.

I always find the more info you give the better advice you will get.

"Mostly be used on freshwater but want a bit of fun aswell" -
What fresh water? A lake or a fast running river? What kind of fun? Bit of speed or thinking you may be able to tow something?

2 adults and a teenager can sometimes weigh in at close to 250kg, different adults and teenager it drops to 190kg

"Would a 10hp 2 stroke (fairly old age I think, but in good nick), or a mid 2000's 6hp 4 stroke be better?" -
That sounds like you have 2 particular OBs in mind.
Will you (perhaps equally important, your partner) be happy with the smell, noise and faff of a 2 stroke - I know my wife wouldn't. However, power to weight ratio can't be matched by a 4 stroke, and maybe one day that will be the route I take.

" Will also be lifting on/off on my own" -
I lift on/off on my own, 47kg OB, but maybe in 5 years time I won't be able to do so, and will need to rethink my setup.
It is nigh on impossible to give advice on what a person can or cannot cope with in terms of weight when it comes to lifting an OB.

So, after all that negativity, if it was my 3.3m sib I would go for a 15hp 2 stroke (Yam?). Lightweight with enough power to be comfortable when 3 up and have a bit of fun but maybe not tow.

Croolis · 19 June 2023, 08:52

My boat is 3.2m.

I use my 2.5hp on a river, two up I get 6-7mph downstream. I can't really go any faster 'cos speed limit, but that doesn't mean I don't want a bigger engine. I'd like to go in the sea, which I'm not going to do with the 2.5hp. And I suspect, though I don't know, that even if I was to keep to 6mph on a river, a 6hp or a 9.9hp would be less noisy.

Plus I don't have a reverse on the 2.5hp, which is a minor PITA.

For me, the question is whether to go up to 6hp, which is physically manageable for me on my own, or 9.9hp which is more desirable but I face serious handling/storage questions around that.

My research has shown me that, if you're not keeping the boat on trolley (I'm not, and even if you are), if you don't have loads of grunt that's more of an issue than the finance or pretty much anything else.

lightning · 27 June 2023, 07:52

We've got a 2.8m boat and initially had a 6hp 4-stroke engine, this engine was fine with two of us and would achieve planing speeds with a bit of effort, where legal.
Speed was around 14mph

I replaced it with a Tohatsu 9.8hp 2-stroke which is the same weight as our 6hp was, that is 26kg

l've had no issues with noise or smell, it's a twin cylinder and happy to troll along at a little over idle speed for hours on the canal.

On the derestricted water the boat will achieve close to 20mph, it plane's instantly with two of us onboard and is great fun.

l would recommend you look for a Tohatsu 9.8 two stroke, they are not available new unless you effectively import one, but do appear second hand,

smallribber · 29 June 2023, 16:45

Quote:

Originally Posted by Fenlander

Hi Steve and welcome to the forum. We have frequently been 2 adults and one slim teen girl in SIBs from 3.4-3.8m. A 6hp will not move you at all well if at sea. A 10hp is about the minimum to plane this load, it's what we have now on a light air floor 3.8 (43kgs) and achieves 15kts.

Having said that if your freshwater use is just the river or restricted lake then the speed limit will easily be reached by a 6hp... even a 4hp.

Note Matt's comment re the weight. Many of the 2-stroke 10hp motors were just detuned 15hp models, the only true light 10hp is the Tohatsu 9.8 2-stroke.

No more better advice than that

Tommy c · 29 June 2023, 17:12

Quote:

Originally Posted by Croolis

My boat is 3.2m.

I use my 2.5hp on a river, two up I get 6-7mph downstream. I can't really go any faster 'cos speed limit, but that doesn't mean I don't want a bigger engine. I'd like to go in the sea, which I'm not going to do with the 2.5hp. And I suspect, though I don't know, that even if I was to keep to 6mph on a river, a 6hp or a 9.9hp would be less noisy.

Plus I don't have a reverse on the 2.5hp, which is a minor PITA.

For me, the question is whether to go up to 6hp, which is physically manageable for me on my own, or 9.9hp which is more desirable but I face serious handling/storage questions around that.

My research has shown me that, if you're not keeping the boat on trolley (I'm not, and even if you are), if you don't have loads of grunt that's more of an issue than the finance or pretty much anything else.

I went up to a 9.8 4 stroke last year. I didn't keep it long. The weight spoilt it for me.
I now have a 6hp and it's heavy enough to be mauling about with in and out of transport.
I've just got a new 3.2 sib and only been out in it once and that was with my other half. I achieved 12mph so I'm guessing I'll get 15mph+ solo. I'm happy with that

User name · 30 June 2023, 09:32

A lot depends on the specific make/models but 4 stroke will generally be better for reliability. 2 stroke are generally more powerful for their size/weight.

Depending on the model, you might need to pre-mix the fuel on the old 2 stroke also. Some outboards will mix the oil with the fuel themselves, but another thing to think about is that there's always the risk that the oil pump/feed might fail and you won't be aware, meaning you'll be running the engine without oil.

If the 2 stroke is indeed quite old and has no records of a rebuild then I'd be inclined to look at the 4 stroke.

As far as power goes, more is obviously better but I use my 3.2m air keel SIB with a Honda 2.3HP, 5HP or 10hp 4 strokes, 2 grown men and some fishing gear onboard and it's still very capable. It's not exactly fast with the 2.3 but it's usable even in light seas and the outboard is light enough that I could carry 2 of them. The 10HP can propel the boat about as fast as I'd like to go in an inflatable, but it weighs quite a lot compared with the smaller 2.3 and 5hp and is maybe better suited if you use and store the boat complete.

lightning · 02 July 2023, 20:16

My post was skipped over but l would say again, the Tohatsu 9.8 two stroke ticks all the boxes for what is needed by the O/P on this SIB.

Aside from the possible environmental issues with these older two stroke engines. The exhaust outlet is under water so l guess that's not ideal.

Steve509926 · 02 July 2023, 20:22

One tends to think we may be talking amongst ourselves, 2 weeks and not a word from Mr Boyle.

Croolis · 02 July 2023, 21:50

I'm reading this thread with great interest. 2-strokes - I'm a former motorcycle courier who looks at anything 2-stroke with revulsion (stinky, noisy, lower reliability), plus, paradoxically, I did environment science at uni so there's the ugggh, nasty factor for me with them lol.

But I don't want to be dealing with 48kg either if I go ~10hp. Plus, I can't afford it this year anyway (single parent).,so I dunno.

But the thread is useful to me chaps, and others no doubt. .

Steve509926 · 02 July 2023, 22:13

Quote:

Originally Posted by Croolis

But I don't want to be dealing with 48kg either if I go ~10hp. Plus, I can't afford it this year anyway (single parent).,so I dunno.

But the thread is useful to me chaps, and others no doubt. .

9.9 Tohatsu /Mercury 4 stroke- 37kg.

I agree 8 - 9 kg heavier than a Tohatsu 2 stroke, but surely it would be a waste 4 years @ uni

Croolis · 03 July 2023, 09:39

I think mebbe I was looking at electric start when I came up with 48kg.

Which beggars another question. I don't mind the idea of another pull start, can totally live without electric start. Less to go wrong in my head. Any reason why that should be a bad idea (e.g. they are hard to pull or something)?

Croolis · 03 July 2023, 09:42

I also see 8hp for £1870 brand new (but don't anyone think I'm buying now, as I say. No money for for that shizzle for months

) .

Never seen anyone talk about 8hp, here or anywhere else. Any reason?

User name · 03 July 2023, 10:03

Quote:

Originally Posted by Croolis

I think mebbe I was looking at electric start when I came up with 48kg.

Which beggars another question. I don't mind the idea of another pull start, can totally live without electric start. Less to go wrong in my head. Any reason why that should be a bad idea (e.g. they are hard to pull or something)?

You'll generally be fine so long as you follow the usual inspection intervals and don't pull on the cord like a maniac, but pull starts do wear out and break. The cord is the common failure point but there's an internal pawl that can break too. With an electric start motor you'll put a lot less wear and tear on the pull start so it'll be in good shape for emergency starts. That said, I run a typical pull start for simplicity.

Trello · 03 July 2023, 11:15

Quote:

Originally Posted by Croolis

I don't mind the idea of another pull start ....they are hard to pull or something)?

Smaller, well-maintained engines are not difficult to start at all. I have a 4 stroke 20HP, which always starts on the second pull - even my 12 year old daughter can start it.

Steve509926 · 03 July 2023, 11:16

Quote:

Originally Posted by Croolis

I think mebbe I was looking at electric start when I came up with 48kg.

Which beggars another question. I don't mind the idea of another pull start, can totally live without electric start. Less to go wrong in my head. Any reason why that should be a bad idea (e.g. they are hard to pull or something)?

If you did a poll of small OB sib users on Ribnet it wouldn't surprise me if it would be close to 90% pull start.

Quote:

Originally Posted by Croolis

I also see 8hp for £1870 brand new (but don't anyone think I'm buying now, as I say. No money for for that shizzle for months

) .

Never seen anyone talk about 8hp, here or anywhere else. Any reason?

Same weight as a 9.9 but less power, personally I'd pay the difference.

Steve509926 · 03 July 2023, 11:24

Quote:

Originally Posted by Trello

Smaller, well-maintained engines are not difficult to start at all. I have a 4 stroke 20HP, which always starts on the second pull - even my 12 year old daughter can start it.

Merc efi are not renowned for starting 2nd pull when cold, more like 4th, and you have a fair bit of compression to overcome. My better half can't start it from cold.

Fenlander · 03 July 2023, 11:38

>>Never seen anyone talk about 8hp, here or anywhere else. Any reason?

>>>Same weight as a 9.9 but less power, personally I'd pay the difference.

Yep for medium size SIB use an 8hp is a bit of an in between size because most engine questions are related to will it plane. You only need a couple of adults and fair bit of kit or to add a smallish teen into the equation and the 8hp will not get you onto the plane whereas a 10hp may well do so.

Our comparisons have seen 8, 10, 15 & 20hp motors on a light 3.8 SIB. With two adults and minimal kit the 8hp did not jump onto the plane easily and only managed a just hanging onto the plane 10.5kts. A 10hp was nippy enough onto the plane with the same load and made 15kts.

Going back a few posts re the 2-stroke thing.... I don't think the relatively small group of leisure use folks with 2-strokes are going to have significant environmental impact compared to other major world considerations. Probably do less damage than the impact of building electric cars. Also portable 2-stroke outboards are super simple and have proved very reliable over many decades. So if a model suits weight vs power then no real reason not to consider one.