Who's 4 Stroke Outboards tend to be smallest (8-10HP)

[davidpbo]

SWMBO would like us to replace our Mercury 8HP 2 Stroke (1989) with a probably new or newish electric start 4 stroke.

The engine sits in a well so dimensions are critical. Who's engines tend to be physically smaller? I am thinking Yamaha the Mercury/Mariner/Tohatsu seem large.
Don't know about Honda and no experience of Johnson or Evinrude.

Critical dimensions are:
Back of transom to back of engine (tends to be bigger than 2 stroke because of valves) I have a maximum of 470mm
Top of transom to top of well.
Top of Outboard Bracket to under locker lid 350mm (Locker is open to the side).

The outboard bracket is the grey shaded bar.



My existing outboard has a breather tube consisting of a length of copper pipe (8mm??) with a single loop (Presumably to allow the exhaust gases to cool) which comes out of the leg and goes through the transom. It looks as though it may have been an aftermarket addition to minimise fume build up in the locker, anyone come across this before?

 

[northwind]

SWMBO would like us to replace our Mercury 8HP 2 Stroke (1989) with a probably new or newish electric start 4 stroke.

The engine sits in a well so dimensions are critical. Who's engines tend to be physically smaller? I am thinking Yamaha the Mercury/Mariner/Tohatsu seem large.
Don't know about Honda and no experience of Johnson or Evinrude.

Critical dimensions are:
Back of transom to back of engine (tends to be bigger than 2 stroke because of valves) I have a maximum of 470mm
Top of transom to top of well.
Top of Outboard Bracket to under locker lid 350mm (Locker is open to the side).

The outboard bracket is the grey shaded bar.



My existing outboard has a breather tube consisting of a length of copper pipe (8mm??) with a single loop (Presumably to allow the exhaust gases to cool) which comes out of the leg and goes through the transom. It looks as though it may have been an aftermarket addition to minimise fume build up in the locker, anyone come across this before?

You are going to struggle to find a suitable engine of sufficient HP. I spent one Southampton boat show going round the stands measuring engines to fit our well. The eventual advise from Tohatsu was to find a second hand 9.8hp two stroke..

The smallest I found was this one:

http://www.selvamarine.com/product.php?line=mot_4t&prod=blackbass-8

However I don't know the brand, and was worried about the availability of spares and reliability.

 

[AngusMcDoon]

I did a rough measurement of my Tohatsu 9.8 & it looks like it will fit, but only just on the height.

 

[davidpbo]

I did a rough measurement of my Tohatsu 9.8 & it looks like it will fit, but only just on the height.

Thank you for taking the trouble to do that. My feeling is that the Mercury/Mariner/Tohatsu 8 and 9.9HP is too close to the measurements I took for comfort.

The Yamaha appears to give a little more wriggle room, but I am interested in other mainstream brands. Unfortunately the dimensions that are really critical to me are not often freely available.

 

[Tranona]

All what you call "mainstream" brands use similar, and in some cases even the same basic engines so you won't find much variation in size with the exception of Selva which has its own unique design. Selva is a very well established Italian make with an equally well established presence in the UK but has never sold in big numbers here as difficult to compete with the Japanese.

Your exhaust vent is indeed an aftermarket, probably home made fitment in an attempt to overcome one of the major potential drawbacks of well installations which is dealing with the fumes from the exhaust pressure release event. Some wells are worse than others, with the worst often physically large engines fitted in confined spaces and running too deep in the water making back pressure worse.

You may get a much better installation using a smaller hp motor which will be both physically smaller and probably produce less fumes. Make sure you get the correct shaft length so that the prop is correctly immersed - that is not too deep. so if the top of the mounting board is 15" or so from the static waterline it is a standard shaft.

 

[TSB240]

I went through this choice with our Trapper Ts 240.
The only 4 stroke of greater than 6hp that came remotely close to both fitting our well and clearing the stern bulkhead was an older version of the Honda.
The newer versions wouldn't.
Anything at 6hp is a single cylinder and in my experience give a very loud thumping vibration making the noise very intrusive.

I settled for a 9.8hp two stroke twin . They are still available and you will see adverts on E bay and Boats and Outboards quite often.. (New and Secondhand but not cheap!)
I still have a spare one, a short shaft, no electric start but with charging coil that I am inclined to hang on to until someone makes me an offer I really cant refuse.........

Currently used very occasionally on a lightweight rib when I get the need for an adrenaline rush!

Tohatsu Tech Sales recommended a leg vent as your OB Helps minimise exhaust fumes in cockpit. Simply drill and tap and fit a hose tail.

 

[davidpbo]

Hi Folks

Thank you for your replies, sorry for the delay in replying, I was on the boat and mobile data reception is hit and mostly miss.
Interestingly I know of a 10 year old Honda for sale might look at that further. I do feel a Yamaha would fit as well.

Thank you also for the information on Selva. With regard to the length of shaft, my current OB is very definitely a long shaft and I am sure most of the ones fitted to Jeanneau Tonics are, I have measured top of bracket to water but will check it and try and see how far the prop is under the water. Obviously a standard shaft would be cheaper and may I suppose cause less exhaust build up because the back pressure would be less ???. Exhaust re-entry into the well from below is limited by what someone eloquently called a "Fanny" two rubber strips which grip the OB leg on either side.

 

[davidpbo]

I am re-visiting this problem and have made a template (cardboard) of the inside of the outboard (Inboard) well.

Does anyone around South Manchester/ Cheshire near Macclesfield have a recent Tohatsu, Mercury, Mariner or Yamaha 4 stroke, 8 or 9.9 HP I could offer it up to see if it a fit is likely? If you do and are willing please PM me.

I will try the local outboard shops as well.

Thanks

David

 

[ghostlymoron]

I'm interested in your 'fanny', I've been thinking of fitting something similar. Is it attached on the underside of the well? Any chance of a picture.

Hi Folks

Thank you for your replies, sorry for the delay in replying, I was on the boat and mobile data reception is hit and mostly miss.
Interestingly I know of a 10 year old Honda for sale might look at that further. I do feel a Yamaha would fit as well.

Thank you also for the information on Selva. With regard to the length of shaft, my current OB is very definitely a long shaft and I am sure most of the ones fitted to Jeanneau Tonics are, I have measured top of bracket to water but will check it and try and see how far the prop is under the water. Obviously a standard shaft would be cheaper and may I suppose cause less exhaust build up because the back pressure would be less ???. Exhaust re-entry into the well from below is limited by what someone eloquently called a "Fanny" two rubber strips which grip the OB leg on either side.

 

[davidpbo]

I'm interested in your 'fanny', I've been thinking of fitting something similar. Is it attached on the underside of the well? Any chance of a picture.

Certainty but not tonight it's ruff out there ?. Boat is on the drive.

 

[davidpbo]

I'm interested in your 'fanny', I've been thinking of fitting something similar. Is it attached on the underside of the well? Any chance of a picture.

Pictures as promised

[/URL][/IMG]

Another here.

http://i1205.photobucket.com/albums/bb425/17234/Boat/OB Hull Entry 1_zpsekgyjxoh.jpg

It is fixed by stainless steel screws. What they go into I am not sure, it may be solid fibreglass or some sort of plastic, the other side of what they go into are within the outboard well. Mounted them on a frame and wedging it in the bottom of the well might be an option I suppose.

The rubber is now 27 yrs old and somewhat perished. New rubber may give a tighter fit around the shaft and less leakage of exhaust fumes from leg back into the outboard well when not moving. Whether it contributes anything to sailing by fairing the well I do not know.

If I replace the engine I will probably at least look at replacing the rubbers.

 

[DownWest]

Suzuki have not been mentioned. As far as I know , they make their own o/bs, so might be worth a look if different to the Tohatsu collection.
Friend has a a version of the pictured 'fanny' used rubber matting aimed at car foot wells and got a closer gap than in the pic. Secured to the hull (cold moulded wood) with ss strips and screws. bit of fairing at the forward end to help water flow.

 

[davidpbo]

Suzuki have not been mentioned. As far as I know , they make their own o/bs, so might be worth a look if different to the Tohatsu collection.
Friend has a a version of the pictured 'fanny' used rubber matting aimed at car foot wells and got a closer gap than in the pic. Secured to the hull (cold moulded wood) with ss strips and screws. bit of fairing at the forward end to help water flow.

Fair comment re: Suzuki I hadn't thought of them.

Of the outboard main distributors, Yahama, Tohatsu and Selva were helpful supplying good drawings with more dimensions than available on the brochure. Tohatsu even supplied without being asked a couple of dimensions which weren't on the drawing (Transom to back and front of engine). Honda declined referring me to dealers which I find annoying when I ask for very specific detailed information.