How are Newer Catalina 27's Designed?
How are the newer Catalina 27's designed? I'd suggest just changing what is needed to match the lastest Catalina 27 design and not more (i.e. if it ain't broke, don't fix it).Catalina has done a marvelous job of improving their boats every year, albeit the 27 is no longer made, how was the last of the 27's designed (excluding 'walk-out' transom if any)?Have you reviewed the International Catalina 27 Association's website's 'technical information' and posed the same questions to their tech writer (http://www.catalina27.org/)?Have other Catalina 27 owners 'fixed' the problem the same way?Would not the 'back pressure' issue also be of concern within the 'water lift' muffler since it will experience the 'under water exhaust exit pressure?What does 'water lift' muffler instructions/requirements indicate about the back pressure of an 'underwater' exit?If diesel engines have no problem with 'back pressure', why do all motor vehicles with diesels have much larger exhaust/tail pipes?Are you sure the problem is a design issue and not just a prop/prop alignment/prop shaft length issue?My Catalina 30 can, with a following sea, when running near full throttle, periodically immerse the exhaust. However, I believe I notice it does it less since I had the prop's blade alignment/pitch checked and re-trued.How bad is your port stern 'walk' in reverse? If it is excessive, the prop pitch could be off, or one or more blades out of 'sync' with each other, causing the 'slapping' effect which caused the port stern-walk, and cavitation.I have also read that if the prop creates lots of 'cavitation', it actually causes the stern to sink down, possibly due to the air bubbles 'hole' created by the cavitation.By the way, on my 30, with a Universal 3 cylinder M25XP, whereas it does have a fiberglass water lift muffler, the rubber exhaust hose does not do a 'loop' on the way to the stern, but it does run high along the port side, just under the rub-rail, on its way to the middle-stern exhaust exit with flap (which is about 5-6 inches above the water when the boat is at rest).I would also echo "JC on Bainbridge's" comment about above the water and visible exhaust exits. I find it very easy on my boat to view the exhaust and verify water is mixing with the exhaust so I then also know my raw water system is working correctly.However, I also installed a neat water flow alarm in my raw water circuit just before the anti-siphon valve, which is just before the mixing elbow and then the water-lift muffler. If my impeller were to fail, of I were to forget to open the thru-hull valve, it sets off my cockpit engine panel alarm (wired it to the 'oil pressure' switch so that either will set-off the panel alarm). It is from Aqua-Alarm and in case your interested, here is the link: http://aqualarm.net/Hope this helps...
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Well, conventional raw water circulating through a heat exchanger both cools the engine's coolant system as well as cools the hot exhaust gasses so they can be sent through a rubber hose out the transom.Keel cooling uses the engine's coolant pump (usually) to pump coolant through an external heat exchanger, the keel cooler and then through the engine. But it doesn't do anything for the exhaust gasses. Most boats with keel coolers use a dry stack exhaust where the hot exhaust exits up though a chase with an air gap and out the top of the boat. These dry stack exhausts use a lot of interior room and can result in soot particles dropping back on the boat. Another disadvantage is the drag of the external cooler so it is only used on displacement hulls.The major advantage is simplicity- no raw water pump and no circulating raw water to corrode exchangers, ruin impellers, etc. It is only really used on commercial boats.Another way of dealing with the exhaust cooling on a keel cooled boat is to use a raw water pump to pump water through an exhaust mixer just like a raw water cooled engine. This scheme is sometimes combined with a hydraulic oil cooler or I suppose the raw water could be used for a lube oil and transmission cooler.Here is a link to Nordhavn's rational for keel cooling with dry stack exhaust: http://www.nordhavn.com/models/fundmentals/exhaust/ David
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