Blocked engine water inlet

[MikadoII]

While running my 3YM30 engine in my marina berth I found the water temperature sky rocketing. It appears that the sea water inlet was blocked with weed or critters. I was able to clear it by connecting a hose from the marina fresh water supply and back blowing it. The thru hull is a simple 3/4 inch TruDesign fitting. The boat will be out of the water in a few weeks and I am wondering if there is a better fitting to avoid the problem in the future. Does anyone have any suggestions please?

[chrisr]

basically no easy answer

best i can offer is to keep an eye on engine temp. as soon as this starts to run warmer than usual, get in the water with a bit of stiff wire or such and clear the stuff out

it'll happen slowly over a period of time and usually easy enough to keep on top of it before it gets critical

cheers,

[boatpoker]

This sets off an alarm the instant raw water flow is stopped. My first purchase on each of the three boats I've bought.
https://aqualarm.net/index.php?main_page=index&cPath=2

[marcjsmith]

if you don't have a screen over the inlet, could you remove the hose from inside, and then use a bottle brush open up the seacock and a quick up down with a quick up down with the brush and release any crud. gonna be messy once you pull the brush out water and crud is going to find it way in your bilge, but maybe easier/safer than diving on the boat.

[cr180]

Not to be confused with the strainer on the inboard side of the seacocks, there are hull strainers that screw to the hull over the bottom of the through hull fitting. There are two types: round with small holes for slow moving boats or elliptical with slotted holes for faster boats. These hull strainers are fitted over engine and generator intakes. I have found them to be effective. Motion through water generally keeps them clear. If foul at dock, running engine in reverse will clear.

[psk125]

Many people find the outboard strainers very effective...at growing barnacles or mussels inside them. They grow so thickly that they can block essentially all water flow. Cleaning them out is difficult because the fitting blocks getting at the whole opening and holds scraped up shells where you can't get at them, furthering future growth. You can't clean from inside because the fitting keeps tools from getting where they need to go. After not having one on our old boat for 24 years and not having any problems, our new-to-us boat came with one. When we hauled at the end of our first season we found the fitting almost clogged with barnacles which were next to impossible to clear out. We removed it and have had no problems with growth since. Marcjsmith's idea for periodic cleaning of the intake seems the best way to go. Running the intake riser up above the waterline allows you to clean it in the water whenever you think it's needed. Not having a fitting there to block the bottlebrush lets everything float or sink away.

[wingssail]

Originally Posted by cr180

Not to be confused with the strainer on the inboard side of the seacocks, there are hull strainers that screw to the hull over the bottom of the through hull fitting. There are two types: round with small holes for slow moving boats or elliptical with slotted holes for faster boats. These hull strainers are fitted over engine and generator intakes. I have found them to be effective. Motion through water generally keeps them clear. If foul at dock, running engine in reverse will clear.

We have a flush grill over the engine intake. We made it ourselves and it is a bit crude but movement of the boat through the water keeps this clean. Only once has it become blocked, when the front edge came loose and a plastic bag became caught. The bag acted as a flap.

The down side of this grill is that you cannot run a brush down from inside to dislodge blocking matter, however, such blockages have not occurred to us.

[wrwakefield]

Just last summer while running the generator at anchor, the raw water intake became blocked by a jellyfish. [I noticed the gen exhaust water splash had stopped, and shut it down right away...]

The boat has external strainers on the hull for engine intake through-hulls, but I was still pulling bits of jellyfish out of the inboard strainer.

Backflushing with pressure water didn't work. I had to fire up the engine and run the prop in reverse to blow the jellyfish off the strainer.

I doubt this would happen while underway, and was surprized it did while sitting still...

Murphy prevailed- to the detriment of the jellyfish...

FWIW

Cheers! Bill

[requiem]

Originally Posted by marcjsmith

if you don't have a screen over the inlet, could you remove the hose from inside, and then use a bottle brush open up the seacock and a quick up down with a quick up down with the brush and release any crud. gonna be messy once you pull the brush out water and crud is going to find it way in your bilge, but maybe easier/safer than diving on the boat.

With a more traditional engine you could, but a saildrive would be problematic.

When it happened to me, I used air, but it occurs to me that hydraulic pressure would likely be more effective. A small rubber fitting to make a seal at the raw water strainer, a bit of tubing, and funnel/syringe should allow for sufficient force.

[Alex A]

MikadoII,

Another option which you may consider is what we have on our boat, and allows you to clear obstructions in the through-hull while in the water without having to get in the water:

From the through-hull and seacock, We have a Tee fitting then a straight section of pipe about 2-3 feet long to above the waterline. The hose to the strainer comes off laterally from the Tee. The straight pipe extends above the waterline and has a cap on it.

To clear any obstructions, we can remove the cap and pass a 3ft broom handle or similar implement down past the tee and seacock and through-hull.

This solution does require that you have some vertical clearance above the through hull.

I've included a small sketch below.

[sailorboy1]

IMO outside hull strainers are problematic. If it clogs you can not really do anything. With just a straight through hull valve you just take the hose off, open the valves, and stick something into it to clear it out.

Yes water comes in during this, it is nothing to be scared about.

[Bowdrie]

Originally Posted by psk125

Running the intake riser up above the waterline allows you to clean it in the water

Exactly.
My set-up has the hose from the seacock going straight up to a T-fitting that is on the strainer inlet.
The branch of the T is on the strainer, downward run to seacock, upward run having a pipe plug that's ~1" or so above normal waterline.
If blockage occurs just unscrew the pipe plug and stick the clean-out tool down thru the hose and seacock.
No muss, no fuss, no water intrusion whilst cleaning.
This also places the removable cover of the strainer a small bit above the WL, allowing cover removal and strainer cleaning without having the strainer flood into the boat.

[MikadoII]

Thank you everyone for your advice.The position of the skin fitting precludes some of the options. I already have a connection for a marina hose but not a means of blocking flow to the engine to stop flooding. That will be fitted.
Boatpoker's suggestion for a flow monitor is great and will be fitted if I can get one in Australia. Once again, thanks.

[Macdyver]

As someone whose done a little bit of hull cleaning, I really can't stand the external hull strainers. It always seems that little bit of shells from mussels or barnacle really like to get stuck inside them. I always go with a standard thru-hull going to an over-sized sea strainer mounted inside the boat.



My experience has been that I've been able to clear whatever clogs come up, just by reaching under the sole boards and opening up the sea strainer. No need to take off hoses or get under the boat. Just need to dive (or snorkel) on the boat every now and again just to check for any barnacle/oyster/tunichate growth inside the thru-hull (but you should be doing that anyway...)

[Pete7]

Originally Posted by sailorboy1

IMO outside hull strainers are problematic. If it clogs you can not really do anything. With just a straight through hull valve you just take the hose off, open the valves, and stick something into it to clear it out.

Yes water comes in during this, it is nothing to be scared about.

We removed ours when we changed the through hulls. The heads inlet also had one. A blockage has only happened once caused by thick blanket weed on the engine inlet. A quick poke with a hacksaw blade cleared it because we could push it right out.