I seem to remember reading a bunch on this topic in some book once. Here
is what I recall…
I assume your bilge lines run out the stern and not the sides of the
boat, as they should. Here the problem is not having the thruhull under
water, as it is for those in the side of the boat when the boat heels.
Here the problem is following waves splashing up in to the thruhull. The
simplest solution for this is to run the hose so that it briefly ascends
from the thruhull, so water splashed up into the thruhull flows back out
the thruhull instead of down the hose into the bilge. Of course this
means the bilge pump has to raise the water that much further and thus
lowers the real GPH output of the pump, so don’t over do it.
Pete
wrote:
10″ sounds low. I’m pretty sure that mine exit much higher than that, but you have me thinking. I’m pretty sure that the transom is at least a foot above the water line, so the only way I think you could have one that low would for it to be mounted below the transom. I’m pretty sure mine are at least 2 feet above the water line and no more than 2 feet offcenter.
I’ve observed that when under power, the stern wave climbs up the transom at least a foot or so as the boat approaches hull speed. If I had a through-hull that low on the transom, it would be under water. Having a pump exit below the water line not only invites flooding, but also restricts the capacity of the pump. This is not good.
If the through-hulls exit near the centerline of the boat and if they are up a couple of feet or so, they would only be submerged for a very short period of time if you got hit with a wave. I’ve run my bilge hoses up high in the locker in a loop. This isn’t vented and doesn’t need to be as long as the through-hull isn’t submerged for long periods of time. From your description, it sounds like yours are lower. All the 424’s are different, but it would be odd for Pearson to have done something so dangerous; maybe a PO screwed up.
I’ve seen vented loops that are made with stepped barbs on them. You cut the thing off at the hose size you need.
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Rich Carter
Original message
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