Outboard Motor Well

[Kelldog]

Greetings to all;
I am considering cutting out a well in my Cross trimaran for my outboard motor. There is a spot where the framework has been built in to do this but was not finished. I have a 5hp 4 stroke that I use ( I need/want a 9.9hp) and with the outboard bracket I use I still have an issue with cavitation in choppy water. Drives me nuts!!!

I would have to rig something that would allow me to raise the motor up when not in use. I don't think I have enough clearance to be able to get the prop completely out of the water but that might be ok.

Any ideas or thoughts on this? My Cross is 28/30 ft. The well is in front of the rudder and alittle to the starboard side...not centered.

Thanks your input

Kelly
S/V Mystic
Long Beach, Ca

[speedoo]

I once owned a 26 ft. monohull that had an outboard well in the cockpit. The fumes the outboard ( a 9.9, coincidentally) generated made the cockpit at best unpleasant, because the location did not permit enough air circulation, especially when there was not enough wind for sailing.

So I would keep that in mind.

PS on edit... I added a bracket on the transom for the o/b..... that's how bad the fumes were.

[Kelldog]

Thanks Speedo;

I should add that it would be in the aft enclosed compartment. Maybe I would need to add some ventilation there.

[speedoo]

Kelldog, for an enclosed compartment, I would seriously consider ventilation AND a substantial blower setup.

[Talbot]

Biggest problem with an outboard in a well, is the trade off between sufficient ventilation for the engine, and getting rid of exhaust smoke.

The further forward the engine, the less of a problem with cavitation (if the shaft is long enough).

I added small wings to my cavitation plate and that definitley improved the ability to operate without cavitation, but then creates a problem with getting it far enough up to avoid dragging in the water.

I have seen one cat where they created boxes in the bridgedeck, these boxes contained the transom for the outboard. when needed the box was hinged down from the front, the engine having already been swung down, and away they motored. When not needed, the boxes were raised, providing better clearance for the outboard.

[Tnflakbait]

Hey Kelly!

It seems like a lot of work to cut a hole for and engine well. It will also add drag. Have you looked into an extra long shaft outboard? You could also modify the existing mount so the engine sits lower when you drop it.

We are in French Polynesia now aboard Aita Pe'ape'a. Message me your email, and when we get our blog set up I can give you the link.

-Tristan

[GMac]

In one of my beasts (31ft mono this one) I have a 9.9 high trust long shaft in a well near the aft end of the cockpit. Works very well, no fumes bit a little noisy.

The OB is mounted onto a wooden plate which is in a alloy U shaped section each side so it slides up and down. The whole alloy slide/frame is hinged in the bottom so I just lift the OB up and then it tilts forward just enough to get clearance of about 3" under the prop. Then I have a little door/flap that drops into the hole which is flush underneth. So then I have zero drag from prop, legs or hole. The flap has a small venturie in it so any water that does sneek in, which it does at speed, just drains out.

Judging by my boat a 9.9hp high thrust 4 stroke would push a 28ft Cat very very nicely. Flat water with a clean bum I cruise at about 6.5 knots at 1.5 lts/hr. Opened right up 8kts and about 3.5lts an hour. Distance crusing about 4.5-5kts at about 2/3rd of a lt/hr. On a 28ft cat it wouldn't have to work at all so be very very cheap to run and still leave pleanty of power to punch into yucky stuff.

The key to it all Kelldog is getting and keeping the prop in the water so whatever you do try to get that prop deep. Further aft you put it the harder that will be I'd think.

[Kelldog]

Thanks for the input guys. I will probably cut down the bracket a bit more and see how that works. then when I haulout again I will take a hard look at it. The cavitation really drives me bonkers though...