dirty transom

[karonoko]

My new (to me) CD 27 has developed soot stains at the waterline of the transom. Any thoughts on how to prevent this?

[Maine_Buzzard]

You might want to look at Super SLick. It's for underwater use, but might be OK right at the edge. We use it for raceboats that will be in the water for 5 days at a time.

http://www.pour-n-restore.com/boat-barrier-wax.htm

[J D]

My guess is you have the original 8 horse ( really 7.5 ) Yanmar I do. Mine did that and at full throttle pores ugly exhaust. I got help from a mechanic and tried several things. First was calibrating the injector pump. The final analysis was that the engine was too small and did this when used beyond it’s ability. I now accept it’s limitation and don’t max the throttle and it does OK. For what this is worth, I hope it helps.

John

[Ron M.]

It may not stop the exhaust stain completly but adding a 2 or 3" section of exhaust hose with a band clamp to the exhaust fitting might do some good. I've seen this on some boats, in fact mine had this when I got it prior to re-powering the ysb-12.

[Duncan]

My guess is you have the original 8 horse ( really 7.5 ) Yanmar I do. Mine did that and at full throttle pores ugly exhaust. I got help from a mechanic and tried several things. First was calibrating the injector pump. The final analysis was that the engine was too small and did this when used beyond it’s ability. I now accept it’s limitation and don’t max the throttle and it does OK. For what this is worth, I hope it helps. John

From other discussions, this seems is a general complaint. My theory has been that the boat is over-propped (i.e. too much pitch). I have a lower-pitched prop I have been meaning to try on it.

I believe the 7 horsepower (continuous) should be enough to drive the boat at hull speed (six knots) in flat water, but the best I get is about 4.5 before it starts to smoke.

[rschlomann]

This also was an issue for me. My CD is on a mooring and the diesel gets little use. We went for an overnight in Oyster in July and had to motor for abt 2.5 hours on the return. Ever since then, no more soot.

[trapper]

My CD25D was getting the old 1gm mustache. We put an extension on the exhaust and it helped but did not solve the problem. Then we noticed the boat was burning oil. We then replaced the head gasket and it helped a lot. But like others, I do not give her full throttle. If I do, she smokes and developes the black hairy transom.

My boat is at a dock and we have to motor a little less than 1 mile before deploying the sails. At one point we thought under use may be the problem, but in the end it was (1) need of a head gasket and (2) a bit under powered.

[Neil Gordon]

My new (to me) CD 27 has developed soot stains at the waterline of the transom. Any thoughts on how to prevent this?

Spend more time sailing!

[Dick Kobayashi]

it can be mitigated but not solved. The solution is well, a solution...of detergent and water. I scrub a couple times a season. I did replace the head on the engine a few years ago and it helped and improved power too. But this is a one lung diesel engine coming up on 30 years old, don't expect too much.

btw the 1GM is a 6.5 hp engine. All the GMs are the same, the higher hp ones just have the cylinder bored out to a larger diameter.

[John G.]

I had the hull of my 25D Algrip painted a few years ago (thanks to a lawyer that put his 10 ton trawler on a mooring rated for something much, much smaller) and although this does not prevent a mustach from growing cleaning is breeze with just a wet sponge. I don't mean to knock R.I. lawyers (too much) but this one solved my mustach problems.

[Loren]

I raised my exhaust outlet by a few inches and most of the problem was pretty much eliminated. The stock location is so close to the waterline that when motoring the resulting squatting of the stern puts the exhaust in the water.

Loren

[RC James]

As an afterthought- check your use of oil. Too much oil will result in burning oil. I have found that my dipstick, when filled to the top mark, is more than the recommended amount of oil by the Yanmar owner's manual.
Am away from the boat and my log right now, but seem to remember that the dipstick was about 1/2 qt pessimistic, leadiing me to overfill the crankcase
Once I reduced the dipstick level to the recommended Yanmar quantity, smoke and moustache have disapearred. On a 1982 25D, the dipstick showed 1/2 low between marks.
Am currrently using a 3-blade 12x9 and can reach hull speed at 2500-2700 w/clean bottom and prop..................but then, haven't been able to get out as much as I'd like over the last 2 years.............still......no smoke w/reduced oil capacity....and engine seems fine.........haven't had to scrape a moustache since then.
25D/1982/#10/smaller GM10 @ 7.5HP

[Duncan]

...Once I reduced the dipstick level to the recommended Yanmar quantity, smoke and moustache have disapearred. On a 1982 25D, the dipstick showed 1/2 low between marks.
Am currrently using a 3-blade 12x9 and can reach hull speed at 2500-2700 w/clean bottom and prop..
25D/1982/#10/smaller GM10 @ 7.5HP....

Those are two very interesting comments.

1. With respect to oil levels, I believe the dipstick reading depends on the angle at which the engine is mounted. Since this angle varies with different installations, it only makes sense to adapt the reading to different individual installations. Thank you for the tip!


2. As far as prop sizing, I was initially surprised that you can swing a prop pitched at 9". I have been thinking of mounting a prop pitched at 7" on my 27. Thinking it through, though, I think this may make sense. Your 6.5 hp is similar to my 7 hp (YSE8), but the 27 is roughly 50% heavier than the 25D. I don't think I've seen weight as a factor in prop sizing calculations. but it seems relevant to me.

[rtbates]

I stopped our 1GM's black stains by running the heck out it.. They absolutely hate being run too lightly for too long..