How big an outboard?

[jamesdestin]

Hi folks. The boat I recently bought came with a mariner 7.5 2 stroke o/b. The boat is a 25ft Coronado. These usually have a well for the outboard but on mine it was filled in before I got it. The inboard has also been taken out (and I don't intend to replace it) and the o/b currently sits on a bracket on the transom. I don't like this arrangement and intend to reinstate the well over the winter. I don't like the current arrangement because the o/b is too heavy for me to manhandle once on the bracket and sticking way outboard. In addition, it just doesn't "look" right. So, once I reinstate the well, the mariner will go in it. In the meantime, I'd like to get a smaller engine to use on the bracket, initially just to get me on and off the pontoon but also to use as a back-up motor once the well is reinstated. My immediate sailing will be in sheltered non-tidal water but next season will be out in the Bristol Channel. So, the question is... How big a motor do I need to make an effective future back-up with the proviso that I'd like it to be as small and light as possible to make it easily managed (and cheap!). I'll probably buy a new one so if anybody has noticed any good deals as they trawl the net, please feel free to let me know! TIA Tony

 

[PaulJ]

My first boat was a Hurley 24 which had an inboard engine but also bracket on the transom for a "backup" outboard. Since I wanted the outboard to double up as the power for the dinghy I opted for a 4hp Merc. The 4hp was too heavy and too powerful for the little dinghy we had but it did a fine job of pushing the Hurley along at about 4 1/2 kts so I would think you need about a 4or5hp though even that will be quite heavy....

Paul.

 

[Evadne]

One way to look at it is in hp per ton. Our boat is generally considered underpowered with about 2hp per ton, although it pushes her around in weather that is too calm for sailing, in and out of marinas etc. with no trouble. 4hp per ton is quite common, for the main propulsion, more is just a waste of fuel on a displacement boat, unless you've got a strong tide to motor against habitually. Like in the Bristol Channel, perhaps?

 

[Talbot]

Try looking at it from a different viewpoint. The 7 is tooo heavy to lift at that distance out from the stern. You are therefore constrained immediately to a 2-stroke engine (better HP/weight) You might get away with a 5hp (Tohatsu is a great choice here as it is the same engine as the other makers but cheaper). However this may be tooo much motor for your tender (would be fun though) The 3.5 Tohatso is a strong engine that may be enough for you, and would also be OK for the tender. It is also a light engine that can be lifted (my wife can lift ours) - however the neutral gear and throttle are both on the engine, so this may be another reason for looking at a different engine

 

[StugeronSteve]

Our last boat, a 25' Dehler trailer sailer, had a BF8 Honda hung on the back. Even with a light of boat and easily driven hull I would not have liked to have had any less power, particularly when trying to motor into anything of a sea. We used morse remote control for the throttle and gears, in order to avoid dangling over the transom at crucial moments.

 

[twisterkai]

About 10 years ago a friend bought a Tankard 24 (quite heavy by modern standards), a sailing boat fitted with a Dolphin 2 stroke inboard engine. For those who don't remember those early abortions of engines, they were fitted with a sail drive clutch, dynastart and a rather unreliable solenoid set so that when you wanted astern, the engine was stopped, a lever (electrical connection) was pulled back and the engine was restarted going backwards!!!! A complete and utter nightmare, especially when manoeuvring in a marina surrounded by large expensive yachts.........

After one or two heart stopping near misses, he fitted an outboard bracket to the transom and used a Tohatsu 3.5hp (actually bought for the tender) which as I recall gave about 4.5knts cruising speed (5.5knts flat out) when there was insufficient wind for sailing. If memory serves, it was fitted with a slightly finer pitched prop than standard, and would run for just over an hour on its internal tank, ie, reasonably frugal.

 

[duncan]

pretty much all small OB have the gear shift on the engine so it' sreally down the throttle position - which in most modes will be pretty irrelevant.

I agree that the actual answer has to be the 3.5 range tohatsu , mariner or merc (all the same). light to handle and stow, powerfull enough to give you some way in most conditions and perfect for most tenders.

As with any compromise don't expect it to be able to take you in the direction you wish to go in any conditions - even your 8 won't do that, but it will be enough to avoid going where you don't want to go (unless you get yourself in a silly position in the first place).

Wouldn't use it to get me off my mooring though - I would alwasys want to know my main engine was happy to start at the beginning of any trip.

 

[jamesdestin]

This is all sounding good guys, what about reverse? The small Tohatsu doesn't have reverse but I think turns 360 degrees? What are your thoughts on that for manouvering?

 

[Blueboatman]

? Put all the money into a nice new Honda 9.9 or Yamaha 9.9 4 stroke ?
..And maybe try it on the existing bracket- the sheer manouevrability and lack of drag/noise/fumes are things to consider on a sail boat ,you can always lift it with a block and tackle arrangement clipped to the backstay.,plus presumably the closed off well is currently extra storage? Sorry ,probably exactly the ''opinion''that you don't want to hear .

 

[Talbot]

easier to turn the thing around 180 degrees than reach the gear change lever!

Dont forget that to use it for this mode you will need to have a long shaft, this will not perform quite as well on the tender, but will be acceptable, whereas the short shaft on the back of the yacht will be continually coming out of the water.

 

[corkonian1]

Surely getting a bigger engine to motor against the tide is futile.
On a displacement hull your top speed through the water is determined by boat length and you cannot go faster than this whatever the tide conditions.
However wind is a different matter and you may be thankful for a powerful engine
to motor away from a lee shore in a strong wind.Also an outboard mounted on the transom will bob in and out of the the water and race in choppy conditions, just the conditions in which you may most need it.

 

[Evadne]

Not strictly true, you have to put disproportionately more power into the water for less gain in speed, but there isn't a hard ceiling as such. (My own boat has a 20' waterline which in theory gives here about 5kt displacement speed, but I have clocked 9-10 knots when seriously overcanvassed in flat water.) The real reason, as you point out, is that the sea is rarely flat, especially when combined with a strong tide, so more power may be desirable.

 

[Talbot]

[ QUOTE ]
On a displacement hull your top speed through the water is determined by boat length and you cannot go faster than this whatever the tide conditions.


[/ QUOTE ]

Nonsense.

However, it does take a lot more power to exceed hull speed.

 

[duncan]

on the tender you turn it 180 degrees

as you emergency auxillary you don't worry about manoevring in that detail - you worry about keeping out of trouble and eventually making it back to the general area off your mooring if your main engine packs up!

 

[Jezlyn]

Be careful to check the size of your outboard well. I have an old Johnson 6Hp on my Foxcub 18 but I have to use it on the stern bracket because there is not enough clearance to get the anti-cavitation plate through the bottom of my outboard well!

 

[graham]

In the bristol Channel you will struggle to fight the tides around the headlands whatever motor you fit.A 4 hp will push you back into the barrage if the main engine fails.

The secret is not to fight the tide.let it help you.Ie if you were off Lavernock point and the tide was starting to ebb you could motor until you run out of fuel or turn around go with the tide and be in Barry harbour in 40 minutes.Chill out until low water and leave on the start of the next flood by the time you get back to Lavernock you will have 3 to 6 knots of tide helping you along.

If you want lightness then get a 2 stroke .4 strokes may be better but usually heavier and much bulkier.

A 4 hp 2 stroke could give service on your dinghy as well as back up to the main engine.

click on my blog link below for some Pictures etc from around the Bristol Channel.