Outboards – designing a well around them

I have been looking at outboards up to 20hp - I obviously want to make the well big enough and strong enough to accommodate a wide range of engines. As you may know my back-up engine is a little air-cooled Honda 2.3.

It sips petrol and never fails to start. I also used to ride Honda motorbikes and my mower is a Honda - never been let down by one yet.


So I have been looking at the Honda long shaft engines - they do a 10hp, a 15hp and a 20hp

It looks as though the 8 and the 10hp long shafts are closely related


the 15 and 20 appear to be more or less the same engine - same bore, same stroke.

the weights are more or less the same as well


So far, so good.

but I am missing some crucial dimensions.  I am sure there are some reasonably accurate profiles of these engines on the web some-where so that we can do the same cad trick we did with the Tohatsu

I need to know how big the cowl is relative to the top of the clamps and the distance from the clamps to the narrowest part of the leg, the width and length of the anti cavitation plate

Also, has anyone got any experience with the charging facility on these engines. My Tohatsu is 6 amps - these bigger Hondas offer 12 amps - does that mean it is twice as good - it does add quite a lot to the price. So it  might be better to go for the lower charging and use that cash to buy solar panels - and who sells solar panels?




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9 Responses to “Outboards – designing a well around them”

  1. 25 November, 2013 at 4:22 amPaul Rogers says:

    Plenty of solar panels on e-bay. I could buy a 100 watt panel here in New Zealand for $200 which is about 106 pounds, I think.

  2. 25 November, 2013 at 9:51 pmoldfatgit says:


    Paul Rogers makes a good point. A 100 Watt panel will charge a 12v battery at about the same current as the outboard, but will be doing it all the time. Your outboard will only be doing so whilst running. Granted that a panel won’t be charging at full power under the clouds of this Sceptred Isle, however they will be doing it when you are not on board as well as when you are. Given small requirements for power it may be a better alternative. However, the great thing about engine charging is that it can be done at a time of your deciding as well as when under way using engine. Probably worth compiling a power budget for the boat listing devices, power consumption and likely durations they will be running each day. This will then tell you in Amp Hours what you need, which will inform your selection of battery and preferred means of charging. Of course on a Centaur you will have plenty of room to fit and carry all sorts of means of charging, including (dare I say it) a generator. May actually be cheaper to fit solar panels and carry a cheap 2nd hand generator for those time when the panels have not done the job. Loads on e-bay.

  3. 25 November, 2013 at 10:42 pmdylan winter says:

    a solar panel thing seems right

    I could also shift it across to Katie L once I have done with the Centaur

    as for power requirements – for the centaur my kids will be aboard

    so that is…. two extra laptops, iphones, mp3 players, speakers, extra cameras….. aaaaaagh!

    I will need extra ballast/weight after removing the engine so I shall start collecting old car batteries

    I have three on Katie L and seldom need to switch over to the second

  4. 26 November, 2013 at 4:57 pmRivercruiser says:


    This link on another forum is about 5 yrs old, so the price is now higher, but this setup works for me.

    Maintain your Battery charge! Do not let your battery go flat. You will significantly shorten the life of your Deep Cycle Battery. I use a $24 solar battery charger/maintainer, hung up in my port side cabin window. It has provided 100% of my power since the spring of 2009 all year round. It has a built in regulator that shuts it down when the battery is fully charged. It also has a built in future that does not let the battery discharge back into the solar panel when there is not enough sun to power the panel. Best $24 I ever spent. I was not expecting much from this panel but it has put out like a champ since I installed it in the window.
    Sunforce 50012 1.8 Watt Solar Battery Maintainer. Here’s a link, I’m not associated with this company or vendor, it’s just the one I found on the net at the vendor I bought it from. I see it’s actually cheaper since I bought it.

    Two lead acid marine batteries and an ‘OFF-BATT 1- BOTH- BATT 2’ switch for outboard charging and the solar panel wired in parallel directly to thebatteries.

    It charges when away from the boat and the switch is in the ‘OFF’ position.

    Probably would not keep up with your camera and internet demand.

  5. 28 November, 2013 at 5:26 pmdylan winter says:

    great link…. downloaded some of those – I think I can probably make a few educated guesses from them

    one thing they have solved for me – I was a bit worried about running the outboard too deep

    no worries

  6. 19 December, 2013 at 6:37 pmkev briggs says:

    I have only solar panel charging on my seawych into two 65ah car batteries, runs radio, depth, nav and cabin lights ( all led) and dvd player for two hrs each evening. Use the boat approx three days per fortnight. always had full batteries when I returned to boat after two weeks away. Panel and regulator form maplins. Panel folds in two for storage, and regulator prevents reverse current at night, prevents over charging and splits power separately to the batteries. regulator was less than twenty pounds. Not sure on the price of the panel, size is about 18″ x 24″ open. newer panels probably more efficient. Bright sunny day it has put in as much as 14ah. dark cloudy days maybe only charging at 100 ma.
    (thank god for spellcheck!!! haha)

    good luck

  7. 10 July, 2016 at 10:13 pmWarren says:

    An engine well added to a westerly pagent.
    Saw this listing for a boat including this section in the listing
    “The motor well is unique, in that it mounts the motor on a track that can elevate the motor and prop completely clear of the water when under sail. The motor is lifted and lowered by a 12v internal winch powered by the motor’s starting battery and controlled by a switch in the cockpit. The motor is equipped with a 4-bladed Hi-thrust prop protected by a surrounding circular ring/shroud. This prop ring serves to push open a pair of spring-loaded �bomb-bay� type doors when the motor is lowered and the doors close up as the motor is raised to provide a smooth surface for less drag when under sail. The motor well is “wet” all the time and the cockpit floor”

    Motor is a 20 hp nissan

  8. 11 July, 2016 at 7:41 pmdylan winter says:

    well spotted warren the web ferret


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