RL24, RL28, and RL34 Trailable Yachts
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Motor breathing problems in RL28
We have a 28 with a 9.9 yamaha through hull and it seems to have problems with air intake as it breathes in exhaust and cuts out especially when going slow in an aft wind. Any suggestions on how normally vented as we have bought boat as unfinished project.
Phil & Cindy 29-Dec-2015    Edit    Delete 
Re: Motor breathing problems in RL28
I had this problem on a Mercury outboard, and I eventually found that the main cause was the idle exhaust which comes out part-way up the leg. When in motion the main exhaust comes out of the prop and is not a problem.
I attached a fitting which I strapped to the leg of the outboard where the idle exhaust comes out. A 25mm flexible tube connected the fitting to a through-transom fitting and the exhaust was expelled outside the well.
If operating the outboard with the well cover in place you will need a large hole cut in the cover with a vent screwed to the top. Underneath I glued some flexible foam that cut to roughly fit over the air intake on the top/back of the cowling. This ensured fresh air was always available to the motor.
Finally, if the well cutout is quite large you might need to make a cover for the back section behind the motor. You would need to make it easy to remove so the motor can be tilted, and some people have made "bomb-bay doors" to keep the water from circulating in the well and slowing the boat. A similar arrangement would also prevent the exhaust from bubbling back into the well when travelling at slow speed.
The design of each would have to change for each brand of outboard but these might give you some ideas.
Keith Merkley 29-Dec-2015    Edit    Delete 
Re: Motor breathing problems in RL28
Hi Phil and Cindy
I have a 15hp honda 4stroke in the well of my RL28. I had the same problem as you and fixed it by making a fitting that I fixed over the little above water exhaust on the back of the leg. This allowed me to attach a hose that went throught the transom so that the gasses were vented outside the well.
This also made the motor very quiet.
Some people have large holes in the transom and covered them with s/s louvres, don't know how they went butI prefer a single 1" hole to a couple of large vents.
p.s. This will only work with a 4 stroke.
Good luck and enjoy your lovely boat.
john lloyd 29-Dec-2015    Edit    Delete 
Re: Motor breathing problems in RL28
Some Yamaha outboards have an optional hose barb that screws into the leg exhaust so you can install a hose downhill and out the stern.

I have an RL24 which has similar issues with its 5hp mercury, I drilled several holes in the engine cover near the air intake so air from the cockpit (not the engine well) could be sucked into the engine. The normal intake is low in the well which is fine to stop water getting in but poor for our installations.

For what its worth, I would drill the holes and put a hose on the exhaust.
greg 29-Dec-2015    Edit    Delete 
Re: Motor breathing problems in RL28
I have already put 2 small louvre vent in the transom and one in top of lid to try and get rid of exhaust, but not enough, the motor well has been extended so the motor can swing up inside fully, as you say could be getting extra fumes from prop as well, it seems to be when slow back to an idle and if wind is coming aft it holds the exhaust in . i will do the hose of exhaust port and barn doors , do barn doors have to seal?
Phil & Cindy 30-Dec-2015    Edit    Delete 
Re: Motor breathing problems in RL28
I can't see barn doors making much difference.

Another option would be an electric bilge blower mounted high and dry in the well discharging through the stern. It could be switched on manually when the engine idle is an issue.
greg 30-Dec-2015    Edit    Delete 
Re: Motor breathing problems in RL28
I have already made a board thats sits flat in bottom of motor well which reduces the amount of turbulence caused by prop but doesnt seal. Will try the hose out one of aft vents and see. Thanks guys for your input much appreciated.
Phil & Cindy 30-Dec-2015    Edit    Delete 

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