outboard well(not centaur!)

[born2sail61]

as part of my refit/project,i'm having to rebuild the engine well. It's been butchered at some point in the boats 51 yr history.badly. I have 2 questions,i hope you can answer. Firstly,how far below the bottom of the hull should the prop sit? Which leads nicely onto q2, what are the relative lengths of outboard engines,long,standard and short shaft? I'm guessing there will be slight variations between different makers,so an average for each length would suffice.i'll probably end uop with a seagull due to financial constraints! Thanks

 

[Tranona]

Just about all outboards are made to the same lengths. Standard shaft 15", Long shaft 21" Extra long (rare) 25". The height is from the top of the mounting board to the waterline and results in the anti cavitation plate being just below the waterline. If your boat was built with the well it will almost certainly be for either a standard or a long, probably the former as a long shaft in a well usually puts the power head too high. Some wells have fixed boards and others have sliding boards so you can raise the motor while sailing.

 

[VicS]

as part of my refit/project,i'm having to rebuild the engine well. It's been butchered at some point in the boats 51 yr history.badly. I have 2 questions,i hope you can answer. Firstly,how far below the bottom of the hull should the prop sit? Which leads nicely onto q2, what are the relative lengths of outboard engines,long,standard and short shaft? I'm guessing there will be slight variations between different makers,so an average for each length would suffice.i'll probably end uop with a seagull due to financial constraints! Thanks

Generally standard, aka short, shaft engines are for a transom height of 15" , longshaft for 20" and extralong 25". Transom height means to distance from the top of the transom or mounting bracket to the water level.
Seagulls are a little longer at 16" for a standard shaft and 21 " for a long shaft ( the Featherweight is the only truly short shaft I can think of at 13")
IIRC Honda quote slightly different dimensions, but as a result of measuring them slightly differently.

This will usually put the anti-ventilation plate ( often incorrectly called the anti-cavitation plate) about two inched below the surface .

With planing hulls the aim is usually to get the AV plate close to being level with the bottom of the transom or a little lower.

I would think in a well the aim would be to get the AV plate level with just slightly below the bottom of the well.

Using a engine too deeply immersed might lead to the increased back pressure on the exhaust making it difficult to start although long shaft and even extra long shaft engines are often chosen for sailing boats.
Drag is also a consideration esp if it cannot be lifted clear of the water when sailing.

Prop pitch is an important consideration when choosing an outboard for a slow displacement speed craft. A low pitch, hight thrust, prop being required

 

[2nd_apprentice]

May I? In my case the waterline is actually in the well (which opens in front of the skeg and rudder) and the Tohatsu MFS6 LS anti cavitation plate is perfectly flush with the bottom of my boat. Tohatsu do sell an ultra long version btw. I always wondered if the prop was actually sitting deep enough. The water in the well almost reaches the auxiliary exhaust ports.

 

[VicS]

May I? In my case the waterline is actually in the well and the Tohatsu MFS6 LS anti cavitation plate is perfectly flush with the bottom of my boat. Tohatsu do sell an ultra long version btw. I always wondered if the prop was actually sitting deep enough. The water in the well almost reaches the auxiliary exhaust ports.

I'd assume that the water level would be in the well.

Having the AV plate flush with the bottom of the hull is just about ideal. You would not want it any higher or very much lower..

So long as the prop stays in the water when the boat pitches it is deep enough. The problem with outboards on brackets on the transoms of sailing yachts is that if the " normal" rules are applied they lift out of the water when the boat pitches and become next to useless. Hence the reason for choosing long or extra long shafts. That's the reason I replaced my original 15" shaft engine with a 20" shaft one. ( the new engine also has a low pitch prop with high thrust Mickey Mouse ear blades and a modified exhaust outlet which discharges higher up so avoiding any increase in back pressure and being sucked into the prop when going astern)

If you don't have any starting problems having the water that high up the leg is not a worry.

Exhaust gases being discharged into the well, or rising into the well when idling, can be a problem for the engine as well as for the crew.

 

[2nd_apprentice]

Thanks VicS!

 

[William_H]

I feel obliged to point out that not everyone loves outboards in wells. I for one prefer an o/b on a bracket on the transom. Yes there are problems in a swell with the o/b rising and falling and this must be countered by having an adjustable height bracket. I have seen the water level rise to touch the power head enclosure when the motor is so low as to give thrust when the stern is out of the water but at the time it seemed to drive OK.
I think the big advantages of o/b on a bracket are ease of lifting the leg out of the water when sailing and the fact that fumes and noise are just a bit further away from the crew. Also you get morte cockpit space. I suppose much depends on whether you consider you have a sail boat or a motor sailer and hence how much you will use the motor. Around our club out of perhaps 20 boats I can think of currently only one has a motor in a well and all the others have it ona bracket including one friend who has a well but prefers a bracket so has the well plugged.
Funny how in UK wells seem almost universal. good luck olewill

 

[2nd_apprentice]

Not really an option on my double ender with stern hung rudder ;-)
If anything I'd prefer an inboard but the cost for such a conversion tends to be as prohibitive as the weight of heavy diesel lumps!

 

[VicS]

I feel obliged to point out that not everyone loves outboards in wells.
.
.
Funny how in UK wells seem almost universal. good luck olewill

I think you may have misjudged the situation. Fairly common maybe but by no means "almost universal".

 

[born2sail61]

thanks for all replies/info. I already have adjustable o/b bracket,it's quite a stretch from cockpit,and the prop clearing the water when pitching is an issue(long story but the day my tiller snapped the prop out of water left me with no steerage and a rnli tow!) also the rudder tends to foul the prop on hard 'lock'. I intend making a slide mount for o/b to get prop out of water when not in use

 

[John the kiwi]

Hi There.
My boat had an OB in a well when i got her. Hated it. Like sailing with the handbrake on. Built it in and gained cockpit space and a good 1/2 knot on average sailing speed.
Tried a transom bracket but prop out of water when pitching and too far to reach controls and so on.

Finally ended up transom hung OB as close to Rudder as possible and linked to rudder via a removable bar so that rudder and OB steer in parallel and the prop doesn't ever bite the rudder blade.
Bonus is maneuverability. My rudder is a pivot blade, so i can steer using the boats tiller(not the OB tiller) with motor alone or motor and rudder blade down or rudder blade alone.
The Honda OB has a tilt position that is nearly horizontal so prop is completely clear when sailing.

Good luck