Catamaran thru-hull water intake placement 101

[sundog]

I'm not too good at 'splaining things, so please bare with me. One preferred location to install thru-hull (underhull) water intakes on a cat has been at the rearmost point of each sponson - nearest the transom. But it occurred to me that on a FE cat the transom may actually lift free of the water, being supported by the bottom of the prop at high speeds. This would seem to interrupt the flow of water just when it was most needed. Wouldn't it make more sense to put them in front of the sponsons, just before the first step up in the hull? This is (almost) always in the water when under way.

The rear location might be a holdover from full sized cats. Their hulls are commonly flat (not including the the steps), so that might facilitate water entry in rear pickups. But notice that on later hobby sized cats the hulls are often tapered - the hull height tapers shorter with every step in the hull - and the transom being shortest. I can see where this would allow the hull to be lifted free of the water by the prop, lowering drag and helping it to acquire those freaky (scale) speeds. So my question is: wouldn't the front of the sponsons (just before the first step) be a better location for underhull water pickups on a fast cat, or am I missing something? Feel free to speculate and think out loud....

[TristanJones]

I've just fitted these..

http://imageshack.us/a/img405/7946/2013011419001751.jpg

http://imageshack.us/a/img18/8964/20130114185951445.jpg

Now you mention it Id say you might be right, I will see how I go with temps and water flow. Easy enough to move/scrap altogether if they don't work out.

[sundog]

I gotta say, those hold more promise than the flush mount types.

[TristanJones]

hopefully they are up to it...

[stadiumyamaha]

I've used some similar to that on a cat that worked very well. I started with them as long as yours and eventually shortened them to where the front most point of them are flush with the hull and the trailing edge had just a small hook in it sticking out about a 1/8". Pulled plenty of water through the lines.

[TristanJones]

Thanks for your input. I will no doubt end up going that way too.

[srislash]

Well Sundog, I must say that a part of me is with you on this concept. My Komodo was the first try with these pickups and this thought did cross my mind. But I did go with the rear pad. If I had to do it to say... a Shocker(used to have one) I would be very tempted to try the forward sponson.The Shocker has the pronounced steps whereas the Komodo has flat steps just like a Geico. The idea behind the steps is to aerate the surface and my thought is it must get some air in the lines. BTW the Komodo is still in testing phase for these pickups.

[TristanJones]

Those pickups I put up are flowing huge amounts of water, though they steer the boat something fierce and create a bloody huge amount of lift so Ive filed them down a lot, hopefully a good fix and still good flow now.
The way the drag of the pickups effected the boat I will have to agree they do definitely suck air at times, though I cant see it being a problem as its very much intermittent (you can see it)
More testing in the morning, I'll be taking the dremel with me this time.

[Mike Caruso]

Those pickups I put up are flowing huge amounts of water, though they steer the boat something fierce and create a bloody huge amount of lift so Ive filed them down a lot, hopefully a good fix and still good flow now.
The way the drag of the pickups effected the boat I will have to agree they do definitely suck air at times, though I cant see it being a problem as its very much intermittent (you can see it)
More testing in the morning, I'll be taking the dremel with me this time.

I guess when you get close to the correct depth you could also use them to help the boat track straight. I can see this might help me on my old mono build to keep it straight without adding trim of the rudder. Gets me thinking and can't wait until spring.
Thanks,
Mike

[sundog]

Though I didn't specify (see, I'm not good at 'splaining), I was addressing a possible problem with the flush mount pickups as pictured below. Obviously, if the pickup exits the hull and can reach the water when the transom lifts free at high speed, then it will have a better chance of scooping up coolant. But as you have found, if the pickup does exit the hull to whatever degree, it can have adverse effects on other characteristics (handling, speed loss, etc). Flush mount, up front would seem to be the preferred way to go. I was hoping this thread would also gain the attention of some senior members who have been building boats for a while, but of course some concepts can take time to absorb, (and I admittedly have a history of 'outside the box' ideas, observations and admissions)!

[stadiumyamaha]

One thing I notice that when putting them on a geico, it creat just enough dead to keep it from bouncing with causing much loss of speed.

[Chilli]

I tried a flush mount pick up in a mono once and it adversly affected the handling of the boat. Went back to the rudder pick up and havent looked back.

[TristanJones]

I've used some similar to that on a cat that worked very well. I started with them as long as yours and eventually shortened them to where the front most point of them are flush with the hull and the trailing edge had just a small hook in it sticking out about a 1/8". Pulled plenty of water through the lines.

Any chance you have a picture laying around of how they ended up?? Id be keen to have a look at what worked for you.
Thanks.

[urbs00007]

forgive me for intruding on your thread but had to reply when i saw your pickups. extreme source of drag . go with flush mount pickups sold on this site.

[urbs00007]

was referring to tristan jones pickups. sundog uses correct ones. thanks