2.5 or 4hp outboard 2.7m tender

[Donheist]

Opinions please. I have a 2.7m honwave airdeck tender and need new ourboard in a rush. I have a choice of 2 - a Yamaha 2.5 and a Yamaha 4hp. Both 4 stroke

Which to get?

Price ok either way. Our family is about 300kg plus shopping fully laden. We only go to and from the boat. No need for planing. Thoughts?

 

[Steve65]

4 hp I would suggest pushing that amount of weight. The 2.5 will push it but given the choice Id go for the 4hp

 

[mrangry]

I have the 2.5hp which I think is 18kg. The 4hp is 28kg according to Google, so depending on how you store the engine this may be a consideration as balancing 28kg onto the dinghy off the back of the boat is harder than 18kg.

 

[Donheist]

Opinions please. I have a 2.7m honwave airdeck tender and need new ourboard in a rush. I have a choice of 2 - a Yamaha 2.5 and a Yamaha 4hp.

Which to get?

Price ok either way. Our family is about 300kg plus shopping fully laden. We only go to and from the boat. No need for planing. Thoughts?

Opinions please. I have a 2.7m honwave airdeck tender and need new ourboard in a rush. I have a choice of 2 - a Yamaha 2.5 and a Yamaha 4hp. Both 4 stroke

Which to get?

Price ok either way. Our family is about 300kg plus shopping fully laden. We only go to and from the boat. No need for planing. Thoughts?

Thanks - very swift replies! I’m heading towards 4 - we have a crane and block to help lower it…

 

[ashtead]

You might find a 6hp is no heavier than a 4 Yam that’s certainly what I found hence we have the 6 and recently installed a crane . I have a retired 2 stroke 3.3 merc awaiting a rehoming which is far lighter. I prefer the 6 once it’s attached to transom on an air deck dinghy but have bought a stand alone tank for reassurance .

 

[Rappey]

You might find a 6hp is no heavier than a 4 Yam

A suzuki df6 ss is 24kg.

 

[Laysula]

3.3 Two stroke.

 

[dunedin]

I have the 2.5hp which I think is 18kg. The 4hp is 28kg according to Google, so depending on how you store the engine this may be a consideration as balancing 28kg onto the dinghy off the back of the boat is harder than 18kg.

Yes, unless have heavy duty davits light weight would be my priority no 1, 2 and 3 !
We used to have a 2.5hp two stroke on our 2.7m dinghy and ideal. Now upgraded to a 3.3hp two stroke to be able to start in neutral with grand kids on.
But the 2.5hp was plenty. Planed solo at over 6 knots if got weight forward, but with a load of people need to go slower to avoid splashing.

 

[B27]

Torqueedo?

If you're not planing then most of the time you won't need full throttle on the 2.5HP, let alone bigger.
If you want to anchor half a mile out and make good progress to shore then you'll want 8 or 15HP.

I have a 2HP, albeit on a slightly smaller tender, and rarely need to use much throttle. When I do, it's because I'm against wind and tide somewhere like Salcombe and we need to be wearing oilies.

I would consider a Torqueedo if the alternative was paying proper money for a new 4 stroke outboard.
Against keeping a 10kg 2 stroke I already have, it's a slightly different question.

 

[ylop]

I think the 4 will be pointless. On a 2.7m dinghy that is not planing you will never the opportunity to use the extra 1.5 horses. If you are amongst moorings / anchorages planing is not really an option even if the 4 opened up that possibility.

 

[Bobc]

Go for the small one. I had a 6hp on my 2.9m rib, and have just sold it and got a 3.5hp to replace it. The 6 was too heavy and we just didn't need the extra grunt.

 

[Tranona]

3.3 Two stroke.

Torqueedo?

If you're not planing then most of the time you won't need full throttle on the 2.5HP, let alone bigger.
If you want to anchor half a mile out and make good progress to shore then you'll want 8 or 15HP.

I have a 2HP, albeit on a slightly smaller tender, and rarely need to use much throttle. When I do, it's because I'm against wind and tide somewhere like Salcombe and we need to be wearing oilies.

I would consider a Torqueedo if the alternative was paying proper money for a new 4 stroke outboard.
Against keeping a 10kg 2 stroke I already have, it's a slightly different question.

Why? when he clearly states the choice FOR HIM is either 2.5 or a 4?

 

[pmagowan]

Get the lightest engine you can. I have never found speed and power to be a requirement for a tender. The smallest lightest engine will be enough to get you faster than rowing and with minimal chance of splashes at the bow. Of course if you use your tender like a car going great distances and trips to various places then maybe other considerations but for ship to shore for average boat small and light is best IMO.

I suspect myself with a pair of oars is considerably less strong than a horse although my technique is better

 

[Zing]

I weighed this question too (sorry) as my spare tender. A 2.5hp is about 13kg. A 4hp is is 23kg. If you have to regularly lift the damn thing in and out of lockers then the lighter one is a lot less effort. I bought a small one.

 

[Baggywrinkle]

This post is for interest only, as the OP has a different set of criteria, but this was my decision making process.

I have a 2.7m ZARMini RIB 9 DL which had a 6hp Mercury 4 stroke engine on it (engine now sold) .... It would plane with one-up and the fuel tank in the bow-locker, but 2 up was not possible.

As already mentioned it depends on your personal usage pattern, we anchor some distance from civilisation quite often, so needed to be able to plane with 2 up and shopping. We also pull water toys with the RIB for kids, not very fast but fast enough to be fun. Wanted something with a bit more power. We also have an engine crane on the stern.

The RIB is rated up to 15hp but a 15hp 4 stroke is heavy (I liked the mercury 15hp but it is 45kg) - so I looked for a better compromise.

There is a formula for theoretical top-speed based on pitch, max rpm, and gear reduction ratio with some conversion factors to deliver top speed in knts. Max planing weight is simply engine power in Hp times 40.

Until recently, the 9,9hp was Carb, which put me off, but it has recently changed to EFI

I created this table to get some logic into the decision ...



I wanted EFI to avoid regular carb cleaning and chokes, I wanted as light an engine as possible, and I wanted to be able to plane with 2-up and shopping.

The Mercury 9,9hp is a lighter 2 cylinder and fortunately, it is now EFI instead of Carb, so I pick it up on Saturday.

Theoretical top speed of 16 knots and planing with up to 331Kg all-up weight is OK, and 38kg will crane onto the stern rail better than the bigger engines.

 

[onesea]

4 hp I would suggest pushing that amount of weight. The 2.5 will push it but given the choice Id go for the 4hp

If non planing I would question that, my regular tender on home mooring is a 11' dorry often coated in growth, kept afloat.
I have a 2.3 and 2.7 inflatables.
All powered by a 3.5 2-stroke,
On the dorry I have never needed full throttle even in depth of winter loaded with tools etc.
The 2.3m inflatable with outboard is over powered rarely above idle, the 2.7 is ok maybe about 1/3 to 1/2 throttle.

The only time I have used the 3.5hp at full tilt was pushing my old trident 24 about, where admittedly it was at its absolute limit.

 

[Zing]

Max planing weight is simply engine power in Hp times 40.

Interesting number, but in my experience in dinghies is miles out. I have a 20hp on a tender and so should plane with 800kg, yet anything over 400kg will not plane. Another tender at 30hp has a weight limit to plane of 550kg and that’s a real struggle. My old one at 40hp would do 550kg easier, but not readily. So I suspect the correct figure is more like 20.

 

[Baggywrinkle]

Interesting number, but in my experience in dinghies is miles out. I have a 20hp on a tender and so should plane with 800kg, yet anything over 400kg will not plane. Another tender at 30hp has a weight limit to plane of 550kg and that’s a real struggle. My old one at 40hp would do 550kg easier, but not readily. So I suspect the correct figure is more like 20.

Can't remember where I got the rule of thumb from. It ties up well with my 6hp Mercury experience though, and a German test of 9,9hp outboards where a 3m aluminium RIB was the test boat.

Will question the dealer on Saturday, they have 15hp in stock too, and if they say the 9,9hp won't hack it, then it'll have to be the RIBs max of 15hp.

EDIT: Using 20 as the factor means my 6hp would not have planed with one-up - 6hpx20=120kg max planing weight

..... but boat 59kg + fuel 12kg + engine 27kg + other stuff 10kg + me 77kg = 185kg and had absolutely no problem planing, even one-up with a fat person (100kg) - two-up with my partner on board (+55kg) it was almost there when we were playing with the weight distribution.

 

[Zing]

Can't remember where I got the rule of thumb from. It ties up well with my 6hp Mercury experience though, and a German test of 9,9hp outboards where a 3m aluminium RIB was the test boat.

Will question the dealer on Saturday, they have 15hp in stock too, and if they say the 9,9hp won't hack it, then it'll have to be the RIBs max of 15hp.

EDIT: Using 20 as the factor means my 6hp would not have planed with one-up - 6hpx20=120kg max planing weight

..... but boat 59kg + fuel 12kg + engine 27kg + other stuff 10kg + me 77kg = 185kg and had absolutely no problem planing, even one-up with a fat person (100kg) - two-up with my partner on board (+55kg) it was almost there when we were playing with the weight distribution.

I’ve also had a little dinghy planing with a 4hp engine at near to 40:1. It’s not a linear thing. We also had a power boat powered up at 8:1. Of course it planed rather easily and that’s a good thing. As your wife will confirm it’s much better to have too much than not quite enough.

A sort of consensus amongst cruisers I know is that 15hp is the minimum you want to get about quickly. So if you are persuaded and if you are going to get a big one get a 20hp Suzuki. Great little engines and weighs the same as the Mercury 15, so a lot more power for no weight penalty. It might be above your tender limit, but you are a grown up and a sensible chap aren’t you?

 

[Chiara’s slave]

Interesting number, but in my experience in dinghies is miles out. I have a 20hp on a tender and so should plane with 800kg, yet anything over 400kg will not plane. Another tender at 30hp has a weight limit to plane of 550kg and that’s a real struggle. My old one at 40hp would do 550kg easier, but not readily. So I suspect the correct figure is more like 20.

I suspect that numerous other factors are at play. I have a Novurania 335 tender, well clearly it doesn’t come with us, maybe it’s a chase boat It’s made of depleted uranium as far as I can tell, or perhaps in the good old tradition or American engineering, add a bit in case there’s a weakness, then give it more power. Regardless, it’s often up to 500kg all up, with a 25hp engine. That’s 20 ratio, it leaps out of the water at half throttle or so, and is utterly bonkers fast in such a short boat. It would, I am certain, stagger onto the plane with much more weight. It’s complicated, I feel.

Our actual haul on board tender is a 2.7, and we have gone electric. It's a leap of faith. Like electric cars, you think it won’t go fast enough or far enough, yet it does. A nominal 1.5hp, you wouldn’t guess that when using it.