Gary , thanks for the info, that helps
.quote from posted question: "Please describe in detail more about that dry exhaust system you have and are redoing. Are you welding in Schedule 80 pipe with a high loop somewhere and where is that? What meta are you using for both the hard pipe as well as the flexible segments? How exactly are you making it so quiet? And what are you doing to keep the
engine room cool enough as well as that aft
cabin (especially when you were in the tropics)? Do you have some sort of shutoff near aft end of pipe? What are you doing to keep those heavy following seas out of it? Are you running the exit
cooling water through and exhaust
cooling jacket before it goes to the
keel cooler. Please describe in more detail how the skeg
keel cooler is designed as well as what structural reinforcement there is for the skeg." end of quote
second quote, from same writer "I do have concerns about the unprotected skeg since there is no keel directly in front of it. So….in addition to my last post questions, have you ever had a collision with anything or floating object?" end of quote
The answers to these questions ,and especially the other questions in the previous
posting are necessarily long. So I'll try to deal with these now, and the others later.
The Skeg: is set into the
hull and capped over as a
coolant tank. There are two steel transverse webs that are welded across the top of the skeg/tank and they run well up onto the curve of the hull(well into the turn of the bilge). In construction, when the boat was sitting on the
hull centerline and the
rudder skeg alone ( before the keels were attached), I felt that the transverse frames needed to be extended farther up onto the hull side, so we did that. Prior to doing that we could induce a little bit of movement by pushing rhythmically on the hull, which was eliminated by the 'web' extension.
There is a warm
coolant hose FROM the engine that is injected into the skeg at the top. The cooled coolant is picked up by a deeper pipe that goes from the cap down to near the bottom of the skeg. Then it goes to a bolt-on
transmission cooler, and thence to the engine.
The 'bus' type
heater is on a separate circuit that is separately valved.
This engine cooling system has always worked well even equatorially, on many occasions.
Exhaust: the exhaust pipe is entirely 1.5" id ss corrugated pipe as per this supplier:
Corrugated Metal Hose
The original similar pipe has lasted about 18 years, but began to leak about one year ago in southern
Chile. ( the carbon monoxide
alarm was never triggered, and it was double checked). Because of my
remote location I was unwilling to disable the engine for the
repair, and I was unable to source replacement pipe at the time. Now i can do this, and am in the throes of the job.
The original pipe was bought for $1 per pound from a metals scrap yard - no such luck nowadays.
It consists of two lengths of 6' and 7'. The 6' length is aft and is aft of the ascendant gooseneck loop, and that explains the shortened life, with likely some seawater entering on occasion. The other proximal length attached to the engine has no
leaks and is fine. I tested it today by filling with
water after
removal from the engine.
There is a ss ball valve in the pipe as it exits the hull through the transom above the waterline. I did have a flapper valve on the end, but it apparently was less than perfect. I now have a 2' extension ouside the hull of heavy hydraulic hose, that after hundreds of hours of running seems to be very heat resistant.
In following seas under sail I put a ziplock bag over the end of the exhaust pipe for
insurance.
There is a gooseneck in the exhaust pipe that ascends to immediately under the cabin overhead (aft cabin) which is several feet above the waterline. Unlike a wet exhaust, there is NO WAY seawater can ever get into this engine, which occurs commonly on many boats.
The entire length of exhaust pipe is covered in thick sewn industrial insulating 'blankets', much as you could see on a fishboat or larger powerboat.
The aft cabin is definitely warm at the end of a day of motoring, which has been wonderful for most of our cruising. However , that said, we have had two major voyages in the tropics with up to four crew aboard and it has not been a problem.
Muffler is a standard steel
muffler made by Nelson, I believe designed for a forklift. It is at the end of the exhaust pipe just before exiting. It needs replacement and I will use the same. It is surprisingly quiet. Separate insulating blanket covers it.
The joints are all sealed ( with thread tape) pipe threaded fittings.
My question is: why should the engine room be any warmer with a dry exhaust than with a usual sailboat exhaust?
Anyways, I do have a large capacity fan that actually sucks air out of the engine room to the outside, that I usually run while under
power. The engine derives fresh air from the bilges.
Skeg and collision: you asked and here is the answer - I have had a number of collisions with this boat, but never with another boat. It has really been tested with hitting rocks and
logs at a good speed on a few occasions. Checked: no damage
I cannot think of an incident where the skeg has taken the brunt of a collision. That would be difficult to arrange as it is really quite protected by the keels. If the boat is on a flat surface it sits only on the keels, with the skegshoe (horizontal 1/2' steel plate that projects out beyond the skeg) about 6'' off the ground. The rudder is another 3 or 4'' higher than the bottom of the skeg.
My greater concern was amongst the icefloes of Patagonia, but more for the prop than the skeg.
I forgot to mention that there is a 1/2 " thick steel web leading from about 18" down the leading edge of the skeg ,forward for about 3' to taper into the centerline of the hull (the main zincs are either bolted or welded to this web, depending on availabililty of a welder).
Once , in Haida Gwaii in 1998 or so, we were swept sideways by a tidal
current in a narrow shallow channel and I think it was the skeg or rudder that arrested us against the rocks of Burnaby Narrows. The rudder is prevented from lifting out of the gudgeons by a 1/2" SS bolt through a pintle.
Probably a greater concern might be the constant working offshore in following seas. Even there, because the
windvane is operating through a rudder trimtab there are quite low loads on the rudder and attachments. The rudder bearings are simple plastic pipe lengths pushed into place in the gudgeons. The pintles are about 1" or 1 1/4" ss bar. I replaced these bearings in
Chile but there was surprisingly little wear after all the thousands of miles.
Check out the attached
photo. It was time to replace the shaft zinc, a standard 1 1/4" donut zinc. I do it about every 6 months ( the hull zincs much less often). I have certainly done it with a snorkel , but if the tidal range is enough ( 3' or more, it doesn't have to be dry, just reachable) and if the water is cold I always put it on the beach. Nowadays, with a greater sense of caution, I have a look at the beach at the preceding low tide.
You can see in the
photo that the beach is smooth but a bit steep. All was well and certainly the rudder and skeg were taking the ground for quite a long time before the keels even touched. This photo was in a lovely spot on the west side of Chichagof Island north of Sitka, called Mirror Harbor. Tricky shallow, rock-strewn entrance. Amazingly 1 hour after we had entered, a 55' glass schooner from Port Townsend with about 7'
draft also entered. Brave chap.
I'll close here, and perhaps describe the sailing aspects another time.
Steve