sea chest

Dear N. A. M. E. : We here at the Practical Boat Owners Forum Homework Assistance Service mostly look after boats that are too small to have this kind of dedicated "sea-chest" structure, instead using direct "through-hull" fittings. Some people on this forum are engineers and know all about larger-scale marine work like this, but most of them are not members of the Homework Assistance Service. Even for a non engineer it's not too difficult to figure out several factors that would be in play here and they're not directly dependent on hull length. Unfortunately, the "Let Me Google That For You" service no longer works so that's all we can do for you today. Happy to help!
 
You need to calculate the maximum flow rate that will be drawn from the sea chest by all services i.e. engine cooling, water maker, maybe air con cooling, air compressor cooling, fire pumps, oil coolers. You then need to establish the minimum inlet pressure, NPSH, for the services that are sucking water. Once you know that, you need to calculate the pressure drop that the inlet grill and filter elements, baffles, if any, will cause due to the maximum volume flow rate as a velocity for the size of the opening. If the pressure drop across the sea chest is high, then the NPSH may be exceeded and pumps stall. Iterate until the size of sea chest is arrived at for the required flow rate. To be honest, a sea chest is sized for still water inside and pressure drop will be very low if grillage area and sea chest is relatively large. Size is likely determined by pipe diameters and stiffening around the hole in the hull rather than pressure loss. If there is more than one inlet pipe in the sea chest, then you need to ensure that the suction at one pipe doesn't impact the flow into the other pipe, and that usually means more space. It must not exceed the frame spacing of the vessel, if so, then add in more sea chests that fit between frames.

Anything is possible, if designed correctly.
 
Also check class rules. A 30m boat in some jurisdictions may be required to comply with a certifying body, who will stipulate design requirements for sea chests e.g. American Bureau of Shipping (ABS), Lloyds, Det Norske Veritas DNV et cetera.
 
RunAgroundHard said:
You need to calculate the maximum flow rate that will be drawn from the sea chest by all services i.e. engine cooling, water maker, maybe air con cooling, air compressor cooling, fire pumps, oil coolers. You then need to establish the minimum inlet pressure, NPSH, for the services that are sucking water. Once you know that, you need to calculate the pressure drop that the inlet grill and filter elements, baffles, if any, will cause due to the maximum volume flow rate as a velocity for the size of the opening. If the pressure drop across the sea chest is high, then the NPSH may be exceeded and pumps stall. Iterate until the size of sea chest is arrived at for the required flow rate. To be honest, a sea chest is sized for still water inside and pressure drop will be very low if grillage area and sea chest is relatively large. Size is likely determined by pipe diameters and stiffening around the hole in the hull rather than pressure loss. If there is more than one inlet pipe in the sea chest, then you need to ensure that the suction at one pipe doesn't impact the flow into the other pipe, and that usually means more space. It must not exceed the frame spacing of the vessel, if so, then add in more sea chests that fit between frames.
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Now you have got that off your chest perhaps you could answer the OP's question - if you actually know the answer & do not have to confuse us with b..x. How do you calculate the volume? & what dimensional inputs do you apply. He did not say anything about additional pipes, pressure above, or below the norm & flow etc. Just "volume"
 
N.A.M.E said:
Can you explain ?
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A vessel of c. 30m is unlikely to have many true sea chests, which are usually found in commercial shipping as in Awol's helpful diagram. It therefore seems wise to assume that NAME's mother tongue is not English (though he is undoubtedly competent), and possibly that his question relates to larger vessels being built overseas without support from a formally qualified naval architect familiar with the calculations that OP seeks . The most likely (single) "sea chest" that springs to mind in context of the OP's question as needing "inputs" is that of the whole hull, and 'displacement' or 'displacement tonnage' is probably the commonest metric used in creating stability programs and hydrostatic curves.

Perhaps the OP could add more information ?
 
I don't know how to calculate the volume, but the area of the top needs to be big enough for fifteen men to climb onto.

If given a bottle of rum - that's one bottle each, not one bottle shared between all of them - their volume should be more than adequate. But the volume of the chest I can't help with. And unfortunately the erstwhile owner of the chest is no longer a member of this forum , ,
 
Easy really if it's approximately rectangular. Height x length x width in metres x1000, result is volume in litres.

corrected.
 
RunAgroundHard said:
Also check class rules. A 30m boat in some jurisdictions may be required to comply with a certifying body, who will stipulate design requirements for sea chests e.g. American Bureau of Shipping (ABS), Lloyds, Det Norske Veritas DNV et cetera.
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I calculated the flow rate of the auxiliary system and tried to determine the cross-sectional area,( A=Q/v) but I don't have a definite value for the appropriate velocity.
and I searched about it but I didn't find anything related to velocity .
I found some guidance but in ice class , I'm not sure if it will work for me or not.
 
Binnacle said:
A vessel of c. 30m is unlikely to have many true sea chests, which are usually found in commercial shipping as in Awol's helpful diagram. It therefore seems wise to assume that NAME's mother tongue is not English (though he is undoubtedly competent), and possibly that his question relates to larger vessels being built overseas without support from a formally qualified naval architect familiar with the calculations that OP seeks . The most likely (single) "sea chest" that springs to mind in context of the OP's question as needing "inputs" is that of the whole hull, and 'displacement' or 'displacement tonnage' is probably the commonest metric used in creating stability programs and hydrostatic curves.

Perhaps the OP could add more information ?
Click to expand...
That's true, and I apologize if my words were unclear, but my experience is still limited. And I believe the size of the sea chest won't have a significant impact on the displacement compared to the overall volume of the tanks right ? , But thanks for pointing that out, I might give it a try.
 
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