water pick up on 31 Cat

[Ran-Dom 32]

Just curious as to other 31 owners, does your boat pick up water from the drive or water pick-ups under the boat like mine. I have newer style bravo drive that have the front low water pickup & side water inlets that are not being used. (block off plate) I thinking of filling in the holes under the boat over the winter when I do my repower. I would think they would scrub a little speed. Does the bravo drive provide sufficient water flow over 100 MPH?

[jbbeard]

I just rebuilt and repowered my boat and use both. The underhull pickups feed the engines and the low water pickups feed the supercharger chillers and also cool the outdrives by passing cold water through them. I have sea strainers attached to the underhull pickups which feed everything else. I still need to adjust the lip angle and the protrusion depth of the lip into the water stream. This needs to be done running using water pressure gauges so as to insure correct pressure at speed. This is the most tricky part when the boat goes over 100 MPH. you have to be verry careful to have enough but not too much water pressure!

[ROTAX454]

Originally Posted by jbbeard

I just rebuilt and repowered my boat and use both. The underhull pickups feed the engines and the low water pickups feed the supercharger chillers and also cool the outdrives by passing cold water through them. I have sea strainers attached to the underhull pickups which feed everything else. I still need to adjust the lip angle and the protrusion depth of the lip into the water stream. This needs to be done running using water pressure gauges so as to insure correct pressure at speed. This is the most tricky part when the boat goes over 100 MPH. you have to be verry careful to have enough but not too much water pressure!

Do I assume that you have these style "in hull" water pickups installed on your boat?
http://www.cpperformance.com/detail.aspx?ID=2565

[ROTAX454]

Originally Posted by jbbeard

I just rebuilt and repowered my boat and use both. The underhull pickups feed the engines and the low water pickups feed the supercharger chillers and also cool the outdrives by passing cold water through them. I have sea strainers attached to the underhull pickups which feed everything else. I still need to adjust the lip angle and the protrusion depth of the lip into the water stream. This needs to be done running using water pressure gauges so as to insure correct pressure at speed. This is the most tricky part when the boat goes over 100 MPH. you have to be verry careful to have enough but not too much water pressure!

These originally were installed on my boat.
http://www.cpperformance.com/detail.aspx?ID=2657

I plan to stick with them unless I can find something better.
Note to all Awesome owners. If you do have an "in hull" design water pickup, it would be wise to remove it/them for inspection. I found several things that needed attention.

1) The hull was not sealed after the hole was cut for the pickup. This was also present on the transom drains too.
2) 3M #101 sealant (or similar style marine RTV sealant) was used instead of the 3M #5200

After removing mine, I found water was present within about 1/2 area of the hole. Very little sealant was present when I removed the pickups. Removed the wood portion and filled with a mix of resin/glas fill. Will re-install the pickup of choice with correct 3M #5200.

Also removed the non sealed small wood platform used for mounting the bilge pumps in the engine compartment (in each sponson just in front of the transom). Sanded and prepped the area for a resin mix to level out this area. Will mount the new pumps using 3M #5200 directly to the floor to insure that most of the water is removed from the bilge floor.

[ROTAX454]

Originally Posted by jbbeard

I just rebuilt and repowered my boat and use both. The underhull pickups feed the engines and the low water pickups feed the supercharger chillers and also cool the outdrives by passing cold water through them. I have sea strainers attached to the underhull pickups which feed everything else. I still need to adjust the lip angle and the protrusion depth of the lip into the water stream. This needs to be done running using water pressure gauges so as to insure correct pressure at speed. This is the most tricky part when the boat goes over 100 MPH. you have to be verry careful to have enough but not too much water pressure!

Great James, you are using sea strainers. Can sure save some big headaches by using them. Add the Merc water relief valve #863208A3 and you can add some water pressure insurance. Installed between your strainer and the sea pump inlet. I am dumping mine thru the transom.

[ROTAX454]

Originally Posted by Ran-Dom 32

Just curious as to other 31 owners, does your boat pick up water from the drive or water pick-ups under the boat like mine. I have newer style bravo drive that have the front low water pickup & side water inlets that are not being used. (block off plate) I thinking of filling in the holes under the boat over the winter when I do my repower. I would think they would scrub a little speed. Does the bravo drive provide sufficient water flow over 100 MPH?

Hey Randy, IMHO I would not recommend dumping the hull pickup for the drive soure of water. You would be surprised at the volume of water needed to supply the sea pump, especially at higher rpm's. If drag is an issue, there are several styles of "in hull" design pickups that are adjustable to the thickness of the hull. See CP Performance is one possible source. I would highly recommend adding a sea strainer. A merc water relief valve is an option worth looking at.