New Thru-Hull for Engine Raw Water

[Harveyhall]

I am thinking of adding a new 3/4" thru-hull to replace the raw water intake through the saildrive on my 2005 Bav 36. 

I am doing this after having a number of mussels lodged in the intake area of the saildrive.  I haven't been able to locate if there has been any discussion on the subject in this forum.  If someone could point me in the right direction that would be great.

Background: I have had the saildrive pulled and replaced the diaphragm in 2020.  I also replaced the ball valve on the raw water intake.

I would love to hear your comments on the subject as well. 
Note: I may just use the new thru-hull for a new wash down pump but ready to change hoses to the engine hose at a moments notice. Not sure..

[Yngmar]

Thought about it for our 40 Ocean. With a switchover valve so I could run the engine from either intake (as normally the saildrive intake is superior as it is much deeper and has multiple smaller intakes in different places of the leg, unlikely to be all blocked).

But upon closer examination, I didn't find a good spot to do this. I didn't want it in the fling area of the propeller due to turbulence and potential high intake pressure. Next to the saildrive leg might be okay, but there's not much room there. Forward of it would be good, but that area is mostly covered by the engine. Aft is occupied by some other stuff and I don't really want a seacock there as it'd be too unprotected. Forward of the engine the keel begins and I don't want to drill any holes in that area.

So I shelved that idea for now 

[Salty]

I used to have problems with mussels entering the sea water intake in the saildrive leg, and initially I wasnt sure whether what I could see from the exhaust outlet to overboard was steam or smoke, but then when the engine over temperature alarm went off, the question was answered. Since then I have always soaked and flushed out the saildrive leg waterways each winter with vinegar. Soaking the waterways also meant temporarily blocking up the seawater inlets to the saildrive, and to do that I made up the kit shown in the photos attached. Using self adhesive tape to cover the water inlets on the saildrive leg was unsatisfactory because the vinegar attacked the adhesive and the tape came off within a matter of minutes. So two plywood blocks cut large enough to cover the side inlets were used, and to each if these I stuck some closed cell foam rubber about eight millimetres in thickness. Closed cell foam stopped the vinegar from reaching the adhesive that held foam to the plywood pads. Two sliding clamps were used to hold these in place over the side inlets. Next was to seal off the small hole inlet in the very bottom of the saildrive leg. For this I used about a two inch long 6mm bolt fitted with two nuts and two washers to clamp a rubber grommet into place. this was then pushed up inside the bottom hole and tightened as needed to secure the hole, but not until all water within the leg had been drained out. Next was to open the saildrive cooling water inlet valve and pour about a litre of vinegar into the seawater filter and leave it for a few days, The longer the better, and this would dissolve the mussel shells and leave the waterway clear. Yes, their relatives did come back, and hence the need to do this every time the boat was lifted out.
Later on I fitted a Nasa exhaust temperature monitor, and this would warn of overheating before damage occurred, though this was primarily fitted to warn me before a newly fitted plastic exhaust silencer might get damaged, and also as a warning if the cooling water valve had inadvertently been left shut.

[Harveyhall]

Hi Salty and Yngmar
Salty- I think I remember reading and trying something similar to your solution the first time I lifted the boat out of the water for painting. I believe it worked somewhat but as your first attempt stated glue from tape I used dissolved and I never tried to duplicate your second solution. I may have revisit if a location can’t be found.
Yngnar - I have been wondering about a suitable location and your reasons are valid for not choosing those locations. I am going to see if on the 36 there is a suitable location and be careful of where I (gulp- leaked another hole in the bottom of the boat).
Hoping still for a magic remedy.

[Vasco]

Hey, I am also looking for a good location for a additional thru-hull 3/4" to have a water intake for a watermaker and a saltwater inlet for the galley.
Our Bavaria is a 40 Ocean and I am trying to find a place in the locker under the sink, a bit lower than the outlets of the sink are located. It will be similar to the waterinlet of the Jabsco WC on starboard and should be nearly under water in all wave and cruising condition. It is important, not to get Airbubbles in the watermaker. Therefor a location close to the Propeller/Saildrive will be not the best place.

- Does the 2005 Bav 36 have a similar constellation?
- Are there any other ideas on a 40 Ocean for water maker thru hulls, considering the risks mentioned by Yngmar?
- Are there any other solution for a watermaker intake available? (intake and Watermakerpump should have a maximum distance of 2m)

In terms of the mussles I was advised by the boat yard to take a wooden stick and poke it through the hole which is vertically going out of the saildrive to scrap the mussels. Yes, I managed to get a lot of this shells out of the saildrive leg.
- aren't they dieing, when leaving them in winter drying out? Do they really need that acid treatment to not survive?
- What is the vinager doing with the aluminium of the saildrive leg?

[Yngmar]

I've teed our watermaker off the saildrive engine intake. With a NRV on the engine side and a shut-off valve on the watermaker side. For a saildrive where it's very important to never suck any air, the very deep saildrive intakes are optimal.

The watermaker manufacturer recommends against this, but doesn't explain why and it's been running with no problems for two seasons now. The NRV prevents the watermaker pump sucking water out of the engine strainer (with the engine off) and causing the impeller pump to run dry for a few seconds, which would adversely affect the impeller's lifespan.

The watermaker has a NRV as part of the installation already, so the engine cannot suck the watermaker side dry (and we usually shut the valve when not in use anyways).

The shut-off valve is also so I can work on the watermarker (when pickling or winterizing) and completely separate it from the saildrive/engine route.

The watermaker manufacturer also recommends against installing the intake on the toilet side of the hull, for reasons of obvious yuckiness.

As for mussel growth in the leg, we've never had any problems since we keep running the engine occasionally (which does it all kinds of good compared to sitting still for months with stale seawater in the pipes). At least every two weeks or so.

The mussels definitely die when drying out, but the corpses remain and must be cleared away if you have any that grew too big to just end up in the strainer. On the 120 saildrive you will not get a stick up or down the leg, but you can get a bendy wire in there or a small bottle brush. Make sure you don't snap it off and lose it inside though!

Still haven't got any better ideas for the intake. Perhaps in the center floorboard of the aft cabin? That would sufficiently aft of the propeller and hopefully still deep enough and there's already a bunch of hoses running from there into the engine room. Not sure the bilge is high enough though?

[Salty]

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In terms of the mussles I was advised by the boat yard to take a wooden stick and poke it through the hole which is vertically going out of the saildrive to scrap the mussels. Yes, I managed to get a lot of this shells out of the saildrive leg.
- aren't they dieing, when leaving them in winter drying out? Do they really need that acid treatment to not survive?
- What is the vinager doing with the aluminium of the saildrive leg?

You have no chance of being able to poke a wooden stick up inside the waterway tube within the saildrive leg, and to be able to achieve anything much with it. The problem is that there are bends in that tube  which the wooden stick will not be able to negotiate. I’ve  tried using a very thin bottle brush which had its bristles attached to bendy wire core, but it would not pass around those bends.  Also the sea water filter on my 36 as supplied with the boat was of a particularly poor design such that if it didn’t go back together exactly as intended, that the mussels could get past the filter, and their shells could even get past the cooling water pump. Indeed on the first occasion that I took the rubber sea water inlet off the heat exchanger, in addition to finding several large chunks of rubber cooling water pump vanes within the entrance to the heat  exchanger, I also found several almost complete mussel shells also within that same space. Yes, I know they appeared too big to be able to get through the cooling water pump outlet slot, but the accumulation of bits of pump vane plus mussel shells had blocked off more than 80% of the heat exchanger tubes. So in my opinion, using a wooden rod pushed up inside the saildrive leg waterway and there by concentrating anythin it had moved that much nearer to where it might cause a problem,  is probably asking for trouble. Hence the decision to use vinegar to dissolve the barnacle shells, and which would also tend to clean out any other accumulations within that waterway. In all honesty, I dont know what vinegar would do to the metals within that waterway, but on the basis that vinegar tastes real good on potato chips, and it doesn't seem to do my internals any harm, then I think the saildrive should survive.

[Harveyhall]

Good conversation on potential cleaning of the water intake.  We floating all year on the west coast of Canada. We use the boat all seasons but still end up with a sizeable amount of barnacles. I too believe that vinegar is not much of a threat as it is a mild acid. It was left in the leg for 2 days while I was repainting the bottom. Cleaning an intake strainer will be a much easier job.

I replaced the saildrive diaphragm spring 2020 so that was the last chance to clean it completely.

As for a new thru-hull location, for my purposes the new hole should be nearer midline of the boat as evidence by the failure of the head pump on a good heal. There may be a slight possibility of running the engine while sailing so that may be important.  On the 36 2005 there is a potential thru-hull area in front of the water tank in the rear cabin (port side). It is parallel with the sail drive so any bubbles or turbulence would be travelling aft from the saildirve.

[geoff]

Having read this thread I started to question my sanity ,not the first time!.  I have been poking a stick up the 120s drive leg for many years . I have now refined it to a length ot 10mm threaded rod  ,about 60cm long . I have just been out to the garage to check the spare leg that I have and the hole in the base of the leg opens out into a long straight void about 5cm across  straight through the division plate into the water cooled base of the gearbox. With a bit of wiggling about the pesky critters get mashed. Geoff

[Yngmar]

Having read this thread I started to question my sanity ,not the first time!.  I have been poking a stick up the 120s drive leg for many years . I have now refined it to a length ot 10mm threaded rod  ,about 60cm long . I have just been out to the garage to check the spare leg that I have and the hole in the base of the leg opens out into a long straight void about 5cm across  straight through the division plate into the water cooled base of the gearbox. With a bit of wiggling about the pesky critters get mashed. Geoff

You're right, I remembered the location of the single hole wrong You can get a stick up there, although I wouldn't use anything like a threaded rod, as there was a coating inside the leg which would be destroyed by that. A wooden stick would be sufficient for smashing any mussels, or just a bottle brush if nothing more is in there.

[richmarshall1957@gmail.co]

I had it done on my 2005 Bavaria 36

[Mirror45184]

The raw water inlet through the sail drive leg also provides some cooling for the oil in the sail drive so would be reluctant to by pass this for any extended period.

[Harveyhall]

Would the aluminum leg traveling through water the same temperature of the water which would flow through to the engine be enough to cool the oil?

[Salty]

You might be surprised at just how hot the oil in the sail drive leg can get. I’ve  never actually measured that temperature, but it can cause the volume of oil within the leg to increase significantly, as I found out once when the oil in the leg had been slightly over filled, and found its way out into the bilge after a run. So I think that Mark makes a very good point about not bypassing the internal waterway within the saildrive leg.

[Harveyhall]

I am going to measure the temperature of the oil at cruising speed, that is a good point. Thanks.

I have decided to install the thru-hull as an emergency water coolant intake.  I plan to place a ‘T’ after the thru-hull and ball valve. One length of hose long enough to connect to the existing water intake filter. This hose will be sealed as well as a separate ball valve which will remain closed unless needed. The other length will lead to a washdown pump feeding two bulkhead fittings both forward and aft. I am happy about this forward wash-down access as we encounter a lot of mud in our anchorages. The rear wash-down location will clean the fish cleaning stand.

I have found a location for a thru-hull close to the engine on my boat. A small space just forward of the aft water tank under the rear berth which will accommodate both the thru-hull and the pump.