How thick is my 2007 310 DA hull bottom? Mounting a raw water strainer

[mobocracy]

I'm planning on adding a Groco RSC strainer over/around my generator raw water intake due to issues with weed ingestion. This requires drilling and screwing fasteners into the hull.

How thick is the hull in that area? Is it thick enough for me to drill out, epoxy fill and then tap for screws without going all the way through, or is it thin enough that I will need to consider through-bolting it?

In theory I should consider at least one through hole for bonding, but as I am in fresh water and this stern drive boat will almost certainly never see anything but fresh water I was hoping to skip this.

 

[Spark600]

The last thru-hull fitting I drill on and 2008 Formula boat it was about 1/2" to 3/4" thick.

 

[Henry Boyd]

The last thru-hull fitting I drill on and 2008 Formula boat it was about 1/2" to 3/4" thick.

Yikes, that’s scary thin. Fortunately Sea Rays are much thicker skinned!

We had a through hull water pickup added to the engine of our 280. It went through one of the through hull pads in the engine bay and the core piece was a couple inches thick. If you are dealing with a factory through hull, there should be plenty of meat.

 

[mobocracy]

Yikes, that’s scary thin. Fortunately Sea Rays are much thicker skinned!

We had a through hull water pickup added to the engine of our 280. It went through one of the through hull pads in the engine bay and the core piece was a couple inches thick. If you are dealing with a factory through hull, there should be plenty of meat.

Yeah, I hope its thicker. 3/4" would surely need to be through bolted and it would make mounting this much harder. My generator intake is pretty close to a stringer.

I really hope I can just drill out blind holes, fill/seal with epoxy and then tap external only fasteners.

 

[b_arrington]

I drilled a hole for a through hull transducer on my my 2006 270 AJ. The hull bottom was probably 1 1/2 - 2" thick and solid fiberglass (no coring). I also did some work on my through hull strainer, replacing the built-in scoop with a standard mushroom thru hull and separate slotted strainer with an opening port. The strainer had a mounting base, and I just used the supplied mounting screws with some sealant. Worked fine.

 

[Mig22]

Moved a pickup around on 380 here’s a picture of the plug that came out....

 

[Henry Boyd]

View attachment 98153
Moved a pickup around on 380 here’s a picture of the plug that came out....

Ours was a little thicker, it had a ¾" plywood reinforcing pad on the inside surface.

 

[Ididntdoit]

heres the plug from my '05 300 da - the thick glass is the bottom, then the faring block covered by another thin layer of glass. does your boat have faring blocks in the bilge? if not, one would be easy to add using a small piece of koosa board and some resin and mat

 

[LastCall350]

I'm looking at doing the same in the spring when I haul the boat out for a bottom job. During the summer when the grass gets thick on our lake I am constantly dealing with a plugged thru hull and also strainer.

 

[mobocracy]

I'm looking at doing the same in the spring when I haul the boat out for a bottom job. During the summer when the grass gets thick on our lake I am constantly dealing with a plugged thru hull and also strainer.

Last season was pretty bad, and I've noticed that lake vegetation has gotten worse in the last couple of years, driven by both a couple of seasons of high rain (drives nitrogen into the lake) and elevated water temps. We saw water temps in the low-mid 80s for a couple of weeks around July 4th, when maybe mid-high 70s would be expected. 80 is usually a seasonal peak, for maybe 1-2 weeks tops. Plus we've been seeing low-mid 70s water temps Memorial Day weekend or early June, when mid-high 60s would be normal.

My strainer in the engine room never got plugged, it was something at the intake. It was also pretty variable, for about 2-3 weeks after initially getting plugged it was fine again, then plugged, then fine, then plugged. I might have guessed a bad impeller if it was consistent and running at planing speeds didn't clean it (which didn't necessarily help, either).

I figure an external hull mounted strainer is going to make significant plugging harder as well as make it more likely to wash off when running the boat fast.

 

[LastCall350]

Last season was pretty bad, and I've noticed that lake vegetation has gotten worse in the last couple of years, driven by both a couple of seasons of high rain (drives nitrogen into the lake) and elevated water temps. We saw water temps in the low-mid 80s for a couple of weeks around July 4th, when maybe mid-high 70s would be expected. 80 is usually a seasonal peak, for maybe 1-2 weeks tops. Plus we've been seeing low-mid 70s water temps Memorial Day weekend or early June, when mid-high 60s would be normal.

My strainer in the engine room never got plugged, it was something at the intake. It was also pretty variable, for about 2-3 weeks after initially getting plugged it was fine again, then plugged, then fine, then plugged. I might have guessed a bad impeller if it was consistent and running at planing speeds didn't clean it (which didn't necessarily help, either).

I figure an external hull mounted strainer is going to make significant plugging harder as well as make it more likely to wash off when running the boat fast.

That makes a lot of sense, may be the same reason we had such a heavy season of vegetation here in TN as well. My pick up was the main culprit as well, I would pull the hose off the thru hull and blow water backwards through the pick up every morning before we went out to clear it. Definitely frustrating, hoping it helps.

 

[b_arrington]

In one of the other groups I'm in, there's been a lot of discussion about fresh water flush systems for engines. Some folks are adding a T inline with the water intake, and some are adding a strainer cap with a flush port attached. Most of these are running back to the cockpit inlet where a water supply can be attached to easily flush the engine.

I mention this because one of the side benefits is that the fresh water could be used to back flush the strainer and the raw water intake. This might be a great way to flush out weeds, either via dock water or using the on-board fresh-water system. Non-hose parts for the installations below can be found at the Seaboard Marine store: https://www.sbmar.com/product-category/general-boat-parts/freshwater-flush/

 

[mobocracy]

In one of the other groups I'm in, there's been a lot of discussion about fresh water flush systems for engines. Some folks are adding a T inline with the water intake, and some are adding a strainer cap with a flush port attached. Most of these are running back to the cockpit inlet where a water supply can be attached to easily flush the engine.

I thought about this. But in my case, it's a generator raw water supply. As far as I know, generator lines don't have a scoop on the hull so you don't flood the cooling line with water while running. Wouldn't this also mean you would want a way to avoid pressurizing the generator side when flushing, too, meaning, another shutoff valve on the generator side of the raw water supply?

 

[b_arrington]

I thought about this. But in my case, it's a generator raw water supply. As far as I know, generator lines don't have a scoop on the hull so you don't flood the cooling line with water while running. Wouldn't this also mean you would want a way to avoid pressurizing the generator side when flushing, too, meaning, another shutoff valve on the generator side of the raw water supply?

Yes, those are reasonable concerns. You're right that generators don't have a scoop to prevent over pressurization when underway.

However, as long as you leave the seacock open the pressure is going to go out through the hull vs. into the generator water intake. Also the pressure from a dockside hose (or boat-side fresh water system) is way less than the water pressure generated when the boat is under way and being forced up a scoop. I personally would not be concerned about over pressurizing the raw water side of the generator and flooding the engine when using a dock-water supply in this way.

The setup is intended so you don't have to close the raw water seacock. You leave it open to do the raw water flush. The majority of the water is will be fresh; and raw water will be pretty dilute. Also the fresh water would back flush the strainer / seacock to flush out those components. That eliminates the need to open/close the seacock when flushing.

On the fresh water shutoff valve, a lot of owners tend to leave it open for ease of flushing. This eliminates the need to dive into the engine space to open/close the valve. The water connection point is mounted high above the waterline - there's minimal risk of an flooding issue, assuming all fittings are properly clamped. Also the engine impeller draws water toward it; therefore the fresh water lines would be under vacuum vs. pressure during normal operations. There's no pressure on the fresh water side.