Low water pickup?

IMHO, this is not the forum to get the best response to your question.

I would look at forums based out of TX as they are waaaaaay ahead with tunnel boats.

You might also talk with Bob's Machine Shop.  They are good people and install aftermarket low water pick ups.

Since you didn't state what size motor, Some Yami's did come with low water pickup's.  I know my 115 had it.

FWIW, Bob's LWPU on a Mercury 25 HP 2 stroke did not perform to one of my customer's expectations.

 

One evening over a few cold ones at a local hangout,
a group of half-adzed backyard mechanics,
discussed the problem of low water pick-ups.
We agreed that unless the impeller is below water level to start,
it's difficult to obtain prime. Air bleed prevents suction.
Our beer-fueled solution was an electric pump,
mounted on the transom, fed by a pickup tube,
with the output fed to the engine by way of an adapter
to the water riser tube. When hull speed became fast enough,
the pressure created by the forward motion of the hull
became greater than that supplied by the pump, the pump turned off,
and as long as the hull was operating at planing speeds,
the engine was cooled by the flow from the pickup.
Kind of rube-goldberg, but we agreed it was do-able.
Too bad none of us ever attempted to build it.
We were too busy fish'n and divin'.

 

Longer ago than I care to admit, I was at a local builder seriously considering one of their skiffs. They had a picture on the wall with the boat running next to a beer can sitting on the sand, not quite to the rim in water. They were buds with Bob's in the early days of R&D. Kind of reminded me of "hold mah bheer and watch this" ;D ;D ;D

Alcohol and redneck engineering isn't always a bad thing. ;D ;D ;D ;D ;D

 

The water pickup even on stock LUs is already below the water pump. So not sure what you guys think is the problem lowering it another 3"-4" like most LWPs?

 

Problem with most intakes, is that they are well below the level of the impeller and housing.
The gaskets/orings that seal the housing aren't that great and allow air leakage.
That means the vaccum pressure isn't low enough to keep the pump primed.
That results in lack of water flow and overheating. Our redneck solution was the electric water pump
that was always below water level and so would continuously feed water to the riser tube.
Low water intakes have to be properly engineered and the flow channel sealed.

 

Brett, my point was that at rest the water level is going rise up the pipe to same level no mater if the pipe starts at the bottom of the cone or on the side of the LU above the cone. This means you are at the same starting point with either system. If the stock unit can handle the vaccum requirements for the stock system it will handle for LWP as well.

Under way it is forced induction to the pump either way stock or LWP.