Outboard size/weight trade off.

[SiteSurfer]

Hi folks.

I've got a 2.9m tender with an air deck and keel, powered currently by a new Honda 2.3 outboard.
The outboard is (we are finding) a touch underpowered with 3 people and bags in, especially when the current is going in an non helpful direction.

I am considering upgrading to slightly bigger in order to make the tender a bit more functional when needing to use it in less benign conditions (ie: from anchor to shore) than simply to a mid river pontoon.

No issue lifting the current 2.3HP engine at all, probably going to fit a single engine davit to the pushpit.

From your experience, I know the weight to power ratio goes up when increasing HP, but how drastic is the change in weight to perhaps a 4 or 5 HP engine? Do the increased couple of horses make enough difference from the baby engine I currently have and is the weight not too prohibitive for hauling over the stern (its a traditional high stern, no swimming platform).

I plan on going to lift a few for myself, but the power difference question is one that can only be answered from experience. Any views on the ideal weight to power advantage in modern outboards? Would prefer a 4 stroke as the last 2 stroke I had was tempremental..

I've looked at a couple of the Mercury ones, but before I go to a dealer to test weigh, wanted to see if anyone had some life experience they could share.

 

[lw395]

I suspect you will find a 5hp engine goes a tiny bit faster and makes bigger waves.
Can you try before you buy?
It's important to get the right propellor.
Possibly your Honda would do better with a finer prop, to allow it more RPM?
An 8hp engine ought to give enough thrust to reliably plane.

Weight wise, it all comes down to whether you want to be able to carry the dinghy and motor up a beach. I do, so I stick with a small motor.
I used to have a 5hp motor, it went well on a light boat, but SWMBO could never reliably start it, which was limiting.

 

[VicS]

Hi folks.

I've got a 2.9m tender with an air deck and keel, powered currently by a new Honda 2.3 outboard.
The outboard is (we are finding) a touch underpowered with 3 people and bags in, especially when the current is going in an non helpful direction.

I am considering upgrading to slightly bigger in order to make the tender a bit more functional when needing to use it in less benign conditions (ie: from anchor to shore) than simply to a mid river pontoon.

No issue lifting the current 2.3HP engine at all, probably going to fit a single engine davit to the pushpit.

From your experience, I know the weight to power ratio goes up when increasing HP, but how drastic is the change in weight to perhaps a 4 or 5 HP engine? Do the increased couple of horses make enough difference from the baby engine I currently have and is the weight not too prohibitive for hauling over the stern (its a traditional high stern, no swimming platform).

I plan on going to lift a few for myself, but the power difference question is one that can only be answered from experience. Any views on the ideal weight to power advantage in modern outboards? Would prefer a 4 stroke as the last 2 stroke I had was tempremental..

I've looked at a couple of the Mercury ones, but before I go to a dealer to test weigh, wanted to see if anyone had some life experience they could share.

Why not look at the websites for the various makes of outboards you might consider. Look at the tech specs and compare the weights of the engines in the relevant power range.

Be prepared to find several makes are the same, because basically behind the badges they are the same.

 

[SiteSurfer]

Thanks, VicS I did some reading and found that Tohatsu is a common badged brand.

My 2.3 is 13KG and generic 5HP's seem to be around the 25-28Kg mark so double the weight.

My question (perhaps poorly phrased?) was in real life, how folks found whether the increase in 2HP was actually worth the weight increase, given that I'm so far from the sea/boat - trying something out isnt really an option, even when we bought the 2.3 from a dealer - there wasnt really an option to test first.

 

[Tranona]

Your dinghy is limited in speed, but of course extra payload affects speed and the Honda will suffer with high payloads whereas the 5hp will enable you to maintain its hull speed.

The biggest drawback with the extra weight of a 5hp is handling it on and off both the dinghy and the parent boat. If you can cope with that and you can make use of the extra power then it makes sense.

 

[SiteSurfer]

Anyone got a view on the Parsun range?

 

[Tranona]

Anyone got a view on the Parsun range?

Run! Copies of Japanese and do poorly in the mag tests as don't produce the power claimed, noisy, difficult to start and reliability problems reported by some.

 

[SiteSurfer]

Your dinghy is limited in speed, but of course, extra payload affects speed and the Honda will suffer with high payloads whereas the 5hp will enable you to maintain its hull speed.

The biggest drawback with the extra weight of a 5hp is handling it on and off both the dinghy and the parent boat. If you can cope with that and you can make use of the extra power then it makes sense.

I think I can make the handling work - obviously, it won't be as easy as the lightweight 2.3. Speed isn't the absolute issue, more the power availability - with the loads we usually have in the dinghy its very underpowered - quite often struggling to make way against the current in the creek we have our mooring in when loaded. Its a 2.9m dinghy too which is quite large - much prefer that over the 2.3m we had originally for a short period (which we bought the outboard for).

 

[CLB]

If you want significantly more power you are going to double the weight, as you have already found out. You could have an extra horse for the same weight, with a 3.5hp two stroke tohastu or, if you decide to accept that 26kg is what you will have to put up with, you may as well look for a two stroke 9.8 tohastu and have four time the power. The worst scenario, imho, is to have a 26kg motor that only delivers 4/5/6hp. You are, of course, going to have to get over your dislike of 2 stroke motors. Personally I find them much more reliable than the modern range of portable four strokes.

 

[SiteSurfer]

You are, of course, going to have to get over your dislike of 2 stroke motors. Personally I find them much more reliable than the modern range of portable four strokes.

I'm prepared to be persuaded, the last 2 stroke I had was an old Volvo thing, circa 1980's.
I've seen several 5/6hp 2 strokes which seem perfectly ok. I just got the impression that 2 stroke was 'out' these days.

 

[SiteSurfer]

Been idly looking at the Torqueedo's. I quite like the idea - but am perplexed that the smaller version is rated against a 1.5HP engine and the larger version against a 3HP.

 

[cmedsailor]

I have still not understood whether you are only looking for a brand a new outboard. If secondhand is also an option a 3,5hp 2 stroke is a vast improvement from the honda.
A couple of years ago I sold my horrible, noisy and extremely weak honda 2hp (yes, people say it's simple and reliable but in any case I hated it) and bought a secondhand 2 stroke Johnson 3,5hp. Much quieter, same weight and a lot more powerful, though it will still not plane a 2,4m inflatable (I was not really expecting this; just wanted some more power and less noise...).

 

[richardabeattie]

I have a 4 horse Malta outboard which is fine (and fairly light) on a 16ft Dabber so I think 5 is a bit OTT for a tender.

 

[Graham376]

Thanks, VicS I did some reading and found that Tohatsu is a common badged brand.

My 2.3 is 13KG and generic 5HP's seem to be around the 25-28Kg mark so double the weight.

My question (perhaps poorly phrased?) was in real life, how folks found whether the increase in 2HP was actually worth the weight increase, given that I'm so far from the sea/boat - trying something out isnt really an option, even when we bought the 2.3 from a dealer - there wasnt really an option to test first.

Our previous dinghy was a 2.9 with airdeck and a Suzuki DF6 4 stroke (27kgs) would usually plane it with 2 of us but not with 40L of water + shopping or bikes. Changed to 9.8 2 stroke (still 27 kgs), steady 17 kts 2 up and no problem carrying extras. Planed if 1 of 3 sits on bow tube but not 4 up. Current dinghy is a 2.9 with ply floor and performs slightly better with same type of engine.

My advice would be to look for a good 8hp or larger 2 stroke but problem is they're around 15+ years old by now and usually sold for a reason.

 

[CLB]

I'm prepared to be persuaded, the last 2 stroke I had was an old Volvo thing, circa 1980's.
I've seen several 5/6hp 2 strokes which seem perfectly ok. I just got the impression that 2 stroke was 'out' these days.

Ah, the old Volvo motor explains it. I have a number of two strokes from reliable outboard manufacturers all dated from the late 90's or noughties and they are more, or at least as, reliable as the brand new 6hp four stroke I bought, or the brand new 2,5hp four stroke I borrowed. As you may guess, I am a big fan of Tohatsu. Just look for one in very good condition that has clearly been well looked after and maintained. Two stoke may be 'out' for environmental reasons, but in the scheme of things I don't see that as a big issue.

 

[Graham376]

Run! Copies of Japanese and do poorly in the mag tests as don't produce the power claimed, noisy, difficult to start and reliability problems reported by some.

+1

I know 2 people who bought Parsuns, both very unhappy with performance and reliability.

 

[lw395]

I think I can make the handling work - obviously, it won't be as easy as the lightweight 2.3. Speed isn't the absolute issue, more the power availability - with the loads we usually have in the dinghy its very underpowered - quite often struggling to make way against the current in the creek we have our mooring in when loaded......

Just how slow is it?
2hp should shove a 2.9m dinghy reasonably.
But if you get into a situation where the drag is really bad, e.g. a lot of transom immersed, then your engine won't rev fast enough to develop 1HP never mind 2.3.
It's worse if the engine is propped for 7 knots on a tiny inflatable.
I've used my 2hp as a 'get you home' standby motor on a mate's 4m rib. To make progress we had to both sit on one side and abit forwards to get the transom out of the water.
The engine would rev fairly well and eventually got us up to about 4 knots. Maybe a tad under that, but more than 3. Certainly better than two old sods could paddle the boat.
So, how fast are these currents and just how slow is the boat?

Maybe a look at the drag factor and trim, and prop size?

Obviously if you are low on power, waves will knock your speed and the engine will take longer to regain speed.

 

[Bouba]

It also depends on the tender itself. Is it easy to row? Changing to an aluminum hull could mean that lower power still translates into more forward momentum. The cost of changing motors could mitigate some of the costs of changing tenders

 

[ghostlymoron]

I've had a 4hp 2stroke on a Leisure 17, a 5hp 4stroke on a Leisure 20, a Honda 2.3 on inflatable and 10' Minipram and also pushed my Mirror Offshore (19') when the engine failed. None of them would plane but that doesn't matter to me. I'd say that to plane a heavy laden 2.9 airdeck will need getting towards 10hp and a 4 stroke is a chunky 38kg. Wouldn't be an option for me as it'd need lifting gear.
(I've also got a seagull featherweight but we don't want to start that again).

 

[jac]

I moved from a 2.5 hp 2 stroke to a 5hp. ( also changed dinghy but that's a different story.)

At that size I wouldn't buy a 4 stroke as the weight is obscene and would really make davits , an engine crane a necessity and if going to that extreme then I would probably go larger still and get a 2T 9.8 - the Tohatsus are allegedly the dogs reproductive appendages.

In terms of speed - 5hp will make our 3.1 airdeck plane with 15.5 stone on board - much more and it struggles but we didn't buy it to plane, more to have plenty of speed / power when conditions were tricky.

I would also point out that most makers will get 2 or 3 engines from the same basic engine block - so maybe a 2.5 and a 3.5 then a 4,56 then a 10 and 15 so for the same weight ( but different cash!) you can have different power.

I would define what you specifically want the engine to do first and then buy the biggest engine in that block size that you can find.

From your description you may get away with the 3.5 but suspect you will probably want more. I would therefore look for a 5 or 6 hp which won't make you plane but will get your heavily laden dinghy moving faster.


A 2t will weigh little more than your existing 4 stroke so if you can find a good one it may be worth going down that route and you will not notice the difference