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#31
02-16-2013, 12:16 PM
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Ok, so the question is; why have bilge vents on an outboard boat?
As Denny (Bushwacker) and Jim (77SceptreOB) mentioned early in the thread, bilge vents allow air to circulate in the bilge to keep moisture levels down. A sealed bilge with even a small amount of water in it is going to create a mini diurnal water cycle. During the day, the hull will heat up and water in the bilge will evaporate. At night, when the hull cools down, the humidity will condense on the inner surface of the hull and the underside of the deck. Polyester based fiberglass is not waterproof. Constant or frequent exposure to liquid water is going to cause it to soak up moisture I can't see that being good for the wood core in the decks and transoms of these boats. In a vented bilge, humid air will be replaced with outside air. The air in the bilge is more likely to be close in temperature to the hull, which should reduce condensation in the bilge. The safety concern over fuel spilled in the bilge has already been discussed. To me it's a lesser issue in an outboard boat. All electrical equipment in your bilge should be labeled "ignition protected" anyway. To me, the reasons for having the vents outweigh the aesthetic considerations. Personally, I like the look. It says "function" in a world where we've sometimes lost track of the reasons we do things. Dave
__________________
Blue Heron Boat Works Reinventing the wheel, one spoke at a time. 
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#33
02-16-2013, 12:58 PM
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It still begs the question, why didn't the 20s at least Center consoles have vents like their big brothers? I have small circular vents inside the boat on the sides but I haven't seen a 20 with the exterior vents. Just curious...
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#34
02-16-2013, 01:17 PM
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Quote:
Everyone has their own opinion on it which is interesting to me. I'm dropping the boat off for paint now ill decide down the road. Idk what imma do with mine yet. Now I'm up in the air about it.
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#35
02-16-2013, 04:56 PM
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A bunch of you guys make some great points imho. Many things mentioned are simple easy concepts that are known by many and I would think and hope are taken into account by most people with an opinion. There's no way to argue against the multiple reasons of there being some benefit to any confined space being able to exchange air let alone in mostly inaccesable bilges and netherregions of most small old polyester boats. Many of which are surrounded by water constantly and some, right or wrong, leak every rain or worse. Not to mention, boats in areas where freezing and expansion can be issues on top of common osmosis, delamination, moisture and rot. Though, I personally do believe it is possible to speculate to the degree it's needed assuming the boat's bilge isn't normally inundated with moisture and the fuel system as a whole is up to snuff, tank and other spaces foamed or not. It's one thing to fear explosion than to respect it and understand what limits it's possibility and the things that have to be 100% to ensure that doesn't happen. If the debate leans more to how the hull vents and lack of the foamed tank and such are more forgiving as the boats slips away from being 100% and into the aging process of "that broke loose", "this crack here", that leak there" then I'd agree though I've seen plenty of trashed SC's too but there tends to be less to get trashed compared to some other boats. Whether or not a fuel tank leaks in 20-30-40 years isn't a big thing to me so personally that's not a concern for me. I also think some people really took care of some of these well built boats and someone definitely can't deny there are a fair amount of fairly original 20-30-40+yo hulls out there. As fun as it is to keep seeing how long you can go on the original floor and transom at some point it's probably gonna need to be done for the majority of people no matter what precautions have been taken or are designed into a boat short of epoxy or vinylester etc. I also think many are rehabbed for multiple reasons using newer, better products that vented or not the hull could go a lifetime without a major rehab if done correctly and sometimes incorrectly even, depending on different variables. Also, when you start to bring up i/b's, i/0's , cabins, fabrics, carpet etc. that brings up other things that can surely be talked about but are also well known.
As far as 20's, early 20sf's had fuel above deck, could that be why there's no vent on those? As stated some later ones have vents, could it be because of fuel below deck? Could it have been because of the desire to just make one hull for multiple models as stated? Could it have been for aesthetics? Could it of just been a change in thought? What about the tweener Potter years that have fuel below and no vent? As stated, I/0 20's had transom vents/ blower for other obvious reasons. My personal feeling is the gunnel rod storage holes especially on the 20's that have the larger cutout in the bow provided some level of ventilation. I also think about how small a 20 is and maybe someone thought a hull vent(s) would do more harm than good or be moot if running through some rough stuff. If I wanted to play devil's advocate to some degree then I would have to ask; If there was such a huge concern and foresight to the moisture end of the of it, then why have uncapped rodholders, why have a lower than deck height bow compartment with a weephole going to the bilge, why have a in deck baitwell/storage that drains into the bilge? As far as fuel vapor, why would there ever have been fuel below deck, why wouldn't every boat have a bilge blower(s)? I think the biggest reasons are probably simple, maybe because everything is a tradeoff but worth the tradeoff within a percieved acceptable margin of safety, durability, reliability, convenience and performance in pursuit of having the least amount of unuseable room, a lower center of gravity and slightly to much larger fuel capacity. Wasn't Mr. Potter on here not to long ago, maybe he can share his thoughts on his era boats? All I know is; Vents, no Vents as long as your boat's not taking on water and you don't have any apparent exposed ignition sources or a fuel smell I am more than willing to stare at and appreciate any of your SC's and let any of you take me out on them too, lol.
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Thank goodness that in the scheme of things you are broke, powerlesss and inconsequential, because with the shortsighted alternatives and idealogy you have you'd be much worse than those you complain about.
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#36
02-16-2013, 08:31 PM
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In a 23 inboard it makes perfect sense. They are the engine intakes. That is how the engine breathes. I would also bet at least one of those vents, probably one of the stern vents has a hose going down into the bilge below the engine oil pan and it's attached to a blower. I am reasonably certain that is why they are on the 20 and 23 IO's. Just adding the vents isn't anywhere near adequate to vent a hull from fuel vapor with out a blower. Especially when it matters. AT START UP after a boat has been sitting and the vapors have had time to accumlate. The blowers are turned on for a few minutes before start up and turned off after the engines fire. Once the boat is underway all the airflow necessary to vent the hull is created through the engine intakes.
My guess is they are there because of the inboard models and they just kept the line looking the same across the board. If you have an inboard boat move the vents to the Center Console or into your liner. It will accomplich the same task and your hull will look cleaner. I/O guys move them to the engine cover or the liner.
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