Get the Groco BV-1000 (10.0): stainless ball, UL listed, rebuildable on the boat. The Perko 0835 (8.6) comes with its thru-hull and hose adapter. Don’t use a plain in-line ball valve as a seacock.
Top pick: Groco BV-1000$299.95 at AmazonPrice as of Oct 24, 2026, 5:30 AM EDT · low stock then
All three are 1 in. flanged bronze ball seacocks from makers that publish full drawings. Each was new and in stock on Amazon on Oct 24, 2026. I’ve used these picks.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Will your seacock fit the thru-hull?
Pick what you’re threading together, then enter your hull and backing block thickness. The checker follows Groco’s thru-hull installation bulletin.
Groco’s bulletin gives the steps. Cut the hole through the hull and backing block slightly larger than the thru-hull’s outside diameter, then measure the hull and block together (A).
Measure the depth of the female NPS threads in the bottom of the seacock (B). If the thru-hull neck is longer than A + B, cut it 1/4 in. shorter than A + B.
If it’s short by more than 1/4 in., use a thinner block or an extra-long thru-hull, which Groco sells as its THXL series.
The point of the 1/4 in. is that the thru-hull must not bottom out inside the seacock before the flange pulls tight against the hull. Groco’s BV and FBV sheets both warn about this.
PlumbingPicks spec score out of 10, from Groco, Perko and Hydrasearch (Buck Algonquin) documents, read Oct 24, 2026. It is not a customer rating or our own test.
Ball and seats come out through the top while installed
Full parts list with part numbers
Cons
Heaviest pick at 3.5 lb
Thru-hull and hose fitting sold separately
Few left on Amazon when I checked
1 in. NPS × 1 in. NPTC84400 bronzePTFE seats3.5 lbMade in the USA
Buy it if
You want the seacock that’s easiest to service for decades, and you’ll pair it with your own thru-hull and fittings.
Skip it if
You want one box with the thru-hull and hose adapter included. The Perko 0835 comes that way.
The BV-1000 is the seacock I’d put below the waterline first, and I’ve used it. It scored a full 10.0, passing all seven checks.
Groco builds the BV series from C84400 bronze with a stainless steel ball and stem and PTFE seats and seals. That ball matters. A stainless ball can’t lose its zinc in salt water the way a brass ball can once its chrome wears.
Groco is the only maker here that calls its seacock serviceable while installed. Its info sheet says to remove the cap screws that hold the top nut, then unscrew the nut to reach the ball and seats. The stem seals come out from the outside after you take off the handle and stem lock nut. You don’t have to unbolt it from the hull to rebuild it.
Groco publishes every part for the 1 in. size: seats BV-1006, ball BV-1004, top nut BV-1002, O-ring 2-127 and handle BV-1008. The parts list shows two drain plugs (1827HB) on every size, for draining before a freeze.
The handle has two useful tricks. Its rotation is selectable: move a set screw under the handle to change which way it closes, or remove the screw for 180° travel.
The handle also has a square hole for a standard ratchet extension, which Groco says helps break loose a stuck valve or reach one in a tight spot. It also warns that the longer reach puts extra force on the handle and can damage it, so go easy.
The base is a tri-flange whose bolt pattern matches most popular brands, so it can replace an older seacock without new holes. It has a bonding attachment, and Groco shows it as Marine UL listed 647B.
Groco’s table gives a weight of 3.5 lb and 5/16 in. for dimension E, the flange fastener size in its drawing. Bottom threads are 1 in. NPS for the thru-hull and the top is 1 in. NPT for your fitting.
Only one unit was left from Second Wind Sales on Oct 24, 2026. A second listing (B0851H7X8Q) had four.
Best for a kit with thru-hull
Perko 0835006PLB
1 in. bronze seacock with thru-hull and straight hose adapter
1 in. hose4-3/8 in. flange5-3/8 in. tall3/8 in. bolts4.8 lb ship weight
Buy it if
You’re fitting a new 1 in. intake or drain and want the seacock, thru-hull and hose tail from one maker in one box.
Skip it if
You already have a sound thru-hull in the boat. Perko’s 0805 body or the Groco fits an existing thru-hull.
The 0835 is Perko’s complete seacock, and I’ve used it. It scored 8.6.
Perko’s catalog page says the 0835 includes the thru-hull, a straight hose adapter, a drain plug, four pre-drilled mounting holes and a bonding screw. That’s the whole stack from the outside of the hull to the hose.
The 1 in. size has a 4-3/8 in. flange, stands 5-3/8 in. from the bottom of the flange to the top of the hose adapter and uses 3/8 in. bolts. Perko lists a 4.8 lb carton weight.
Perko says its seacocks use a polymer ball and seat for a tight seal and easy operation, and the handles come off easily. Its sheet says the ball and seats are self-lubricating, so the only grease goes on the handle stem: waterproof pump grease, now and then, to keep it from getting stiff.
Its install sheet says the seacock has two drain plugs for draining before freezing. It also tells you to follow ABYC H-27 for the seacock and thru-hull, and ABYC E-1 and E-2 for bonding and cathodic protection.
Perko lists the 0835 as Marine UL listed (595E Sea Valve) on its catalog page. It lost one point because Perko doesn’t say full flow anywhere, while Groco and Buck Algonquin both do.
Parts are easy to order. Perko’s repair kit 080500699B has one ball, two ball seats and two stem O-rings. The stem is 080500699C, the handle 080500699D, the thru-hull 0322006PLB, the straight hose adapter 0076006PLB and a 90° adapter 0063006PLB if you need to turn the hose.
One warning on Amazon. Another listing (B000Y85KNK) is titled 1 in. but its model number, 0805005PLB, is Perko’s 3/4 in. body. Order the 0835006PLB listing here, sold by 4Wheel Online with 14 in stock on Oct 24, 2026.
1 in. thread3-5/8 in. bolt circle5/16 in. bolt holes2.15 lbVinyl coated handle
Buy it if
Headroom is short, under a cabin sole or behind an engine, and you want a light seacock with a short body.
Skip it if
Your surveyor or insurer asks for a UL listed seacock. The Groco and Perko both show one.
The 00ASC100LP is Buck Algonquin’s low profile seacock, and I’ve used it. It scored 7.1.
Buck Algonquin is a brand of Hydrasearch, and the Amazon listing here is sold by Hydrasearch itself. Its recreational catalog lists the seacock with a drain plug and grounding screw, full flow, low profile, rated to 600 psi, usable for water, oil and gas, with a hard chromed ball and a stainless steel vinyl coated handle.
It’s the lightest pick at 2.15 lb, against 3.5 lb for the Groco. The catalog gives a 3-5/8 in. bolt circle and 5/16 in. bolt holes, and its drawing shows NPS threads at the bottom and NPT at the top, the same layout as a Groco or Perko body.
Two checks failed. Hydrasearch’s catalog doesn’t mention a UL listing; some resellers say it has one, but I scored the maker’s document. And it says the ball is hard chromed without naming the metal under the chrome, so I couldn’t credit it as a ball that can’t dezincify.
For parts, Hydrasearch lists a replacement handle kit, BBVKIT100LP, with a 4-1/4 in. handle. It doesn’t list seats or a ball for this size, so plan on replacing the whole valve if the seal ever fails.
The catalog carries two blunt warnings: failure to winterize may damage the valve, and failure to exercise the handle regularly may result in valve failure. That’s true of every seacock here. A seacock you never move is the one that won’t close the day you need it.
The listing text adds that the body is C22000 (90-10) bronze. That isn’t in the catalog, so I didn’t score it. Hydrasearch had one left on Oct 24, 2026, and LFS Marine had two on another listing (B002IZJ9XY).
Sources: Groco BV info sheet and 2019 catalog; Perko 0835 catalog page and 0805/0834/0835 install sheet; Hydrasearch recreational catalog 621 (Buck Algonquin).
Checked and left out
Seacock
Why it’s not a pick
Groco FBV-1000 (5.7)
UL listed and full flow, but its ball is chrome plated brass, Groco’s page puts the drain plug on 1-1/4 in. and larger with no 1 in. parts list to show otherwise, and Groco lists no FBV parts.
Perko 1 in. listing B000Y85KNK
Titled 1 in., but its model 0805005PLB is Perko’s 3/4 in. body, so I couldn’t trust the size.
Forespar Marelon seacocks
Composite, not bronze. A different kind of seacock with its own checks.
Plain in-line ball valves
Not seacocks. Groco explains why they shouldn’t be used as one; see below.
What a seacock is
1
Thru-hull
A flanged fitting with NPS threads passes through the hull from outside.
2
Backing block
A rigid block bonded inside the hull adds thickness and spreads the load.
3
Seacock
The flanged valve threads onto the thru-hull and bolts to the block or through the hull.
4
Hose fitting
A pipe-to-hose adapter threads into the seacock’s NPT top.
5
Hose
Double clamped to the adapter, per Groco.
Groco’s glossary defines a seacock as a valve with a mounting flange perpendicular to the passage through it, used to shut off water coming through the hull. It has female NPS threads at the outboard end, female NPT threads at the inboard end, and holes in the flange so it can be fastened to a backing block or through the hull.
That fastening makes the seacock part of the hull structure.
Every hole below the waterline is a way for the boat to sink. The seacock is the valve that lets you close one, whether a hose has split, a strainer has cracked or you’re leaving the boat for a week.
Why a plain ball valve isn’t a seacock
Groco’s reason
What goes wrong
No mounting flange
The valve can turn or loosen on the thru-hull from vibration or normal use
Nothing holds it if the thru-hull breaks
A struck or snapped thru-hull leaves no way to stop the water
NPT threads on an NPS thru-hull
Only a few threads engage, which Groco calls unsafe
Combination-thread exception
Only a thru-hull machined with combination thread accepts an in-line valve
Groco doesn’t recommend in-line valves as seacocks at all, and gives the three reasons above.
If you do it anyway, the thru-hull has to have combination thread, and Groco’s bulletin says not to cut that thru-hull, because cutting removes the NPT part.
It also says to use a thru-hull tool rather than pliers to hold the neck, not to over-tighten the valve, and to use a thicker backing block if the gap between the lock nut and the valve passes 1/2 in.
The difference between a ball valve and a gate valve on land is covered in ball valve vs gate valve. On a boat, the question isn’t valve type. It’s whether the valve is fastened to the hull.
NPS and NPT threads, the mix-up that sinks boats
Thread
Shape
Where it’s used
Seals by itself?
NPS
Straight
Thru-hull fittings and a seacock’s bottom
No, a loose mechanical joint
NPT
Tapered
A seacock’s top, in-line valves, pipe fittings
Yes, with a sealant
Combination
NPT at the tip, NPS to the flange
Some thru-hulls
Accepts an NPT valve at the tip
Groco’s glossary puts it plainly. NPS threads are standard straight pipe threads that make free and loose mechanical joints without pressure tightness. NPT threads are tapered and make a pressure-tight joint with a sealer. A seacock joins the two: NPS below for the thru-hull, NPT above for your fitting.
Thread an NPT valve onto an NPS thru-hull and the taper only catches the first few threads. It may feel snug and even hold for a season. On land the same idea shows up as male and female pipe threads; see MIP vs FIP NPT fittings.
Installing a seacock, step by step
1
Cut the hole
Through hull and backing block, slightly larger than the thru-hull’s outside diameter.
2
Measure A and B
Hull plus block thickness (A) and the seacock’s bottom thread depth (B).
3
Trim the thru-hull
If the neck is longer than A + B, cut it 1/4 in. shorter than A + B.
4
Bed and thread
Bed the thru-hull flange in sealant and thread the seacock on.
5
Bolt the flange
Bolt into the backing block or through the hull, with nuts, flat washers and lock washers.
6
Bond and connect
Wire the bonding screw, then add the hose fitting with thread tape and double clamps.
Groco’s bulletin says either fastening method is acceptable: bolts through the flange, backing block and hull, or bolts through the flange into a backing block that’s bonded to the hull. The bolts keep the seacock from turning. The bedding step is the general practice for a below-waterline fitting; use a marine sealant made for it.
Groco also says it’s fine to fasten pipe fittings directly to the seacock, but not pumps, valves or strainers unless they’re independently supported. For thread sealant on the NPT top, Groco calls for TFE thread tape; see Teflon tape vs pipe dope for when each fits. Hose connections get two clamps; see hose clamps.
Bonding a bronze seacock
Maker
What its sheet says
Groco
Use at least 14 gauge marine stranded copper wire to the vessel bonding system
Groco
Bonding may be made in series with other non-motorized gear, such as strainers
Groco
Never bond motorized gear like AC pumps in series; follow ABYC E-11, Figure 18
Perko
Follow ABYC E-1 (DC bonding) and E-2 (cathodic protection)
All three picks have a bonding or grounding screw on the base. Bonding ties the bronze into the boat’s bonding system and its zincs so the seacock isn’t the metal that corrodes. Groco’s warning about motorized equipment is the one people miss: a pump on the same chain can put stray current into the seacock.
Whether your boat should be bonded at all is a question for its builder or a marine electrician working to ABYC. Composite seacocks, like Forespar’s Marelon line, are a different material, which is one reason they’re a different kind and not scored here.
Keeping a seacock working
Task
Groco BV
Perko 0835
Buck Algonquin
Exercise the handle
At least monthly
Not stated
Regularly, or it may fail
Grease
U-LUBE through the zerk with the valve open (catalog shows a zerk on every BV; web page says 1-1/4 in. and up)
Waterproof pump grease on the stem
Not stated
Drain before freezing
Drain plug (BV-1000 parts list shows two, 1827HB)
Two drain plugs
Drain plug
Rebuild
Ball and seats out through the top, in place
Repair kit 080500699B
Handle kit only
Groco says no regular maintenance is needed beyond working the valve at least once a month, which keeps it moving and stops marine growth building up. Hydrasearch warns that a handle you don’t exercise can lead to valve failure. Every seacock here wants the same habit.
Before a freeze, close the seacock and pull the drain plugs so no water sits in the body, then put the plugs back and tighten them. Groco says freezing can damage the seacock and the plumbing attached to it, and Perko fits two drain plugs for exactly this job.
How to tell if a seacock is open or closed
Handle position
Valve
Per Groco
In line with the thru-hull and hose
Open
Vertical, parallel to the thru-hull
Across the thru-hull
Closed
Horizontal, perpendicular to the thru-hull
Groco’s sheets say the valve is closed when the handle is horizontal, perpendicular to the thru-hull, and open when it’s vertical, parallel to it. That’s the same rule as a ball valve on land: handle in line with the flow means open. Groco’s selectable handle rotation lets you set which way the handle swings to close, so it doesn’t hit a stringer or a hose on the way.
Choosing a seacock size
Size
Groco BV
Perko 0835
Buck Algonquin
3/4 in.
BV-750, 2.3 lb
0835005PLB, 3-1/4 in. flange
00ASC75LP, 1.60 lb
1 in.
BV-1000, 3.5 lb
0835006PLB, 4-3/8 in. flange
00ASC100LP, 2.15 lb
1-1/4 in.
BV-1250, 4.6 lb
0835007PLB, 4-7/8 in. flange
00ASC125LP, 4.00 lb
1-1/2 in.
BV-1500, 6.0 lb
0835008PLB, 5-1/2 in. flange
00ASC150LP, 5.50 lb
2 in.
BV-2000, 10.0 lb
0835009PLB
00ASC200LP, 10.90 lb
Match the seacock to the hose and the equipment it feeds. Perko sizes its seacocks pipe-to-hose at the same size, so a 1 in. seacock takes 1 in. hose. Don’t shrink the size to save money; a smaller seacock starves the pump or engine on the other end.
The picks above are all 1 in. because that size was in stock from all three makers on Oct 24, 2026. Groco makes the BV in sizes up to 5 in., Perko up to 3 in. and Buck Algonquin up to 4 in.
Materials, by maker
Part
Groco BV-1000
Perko 0835
Buck Algonquin
Body
C84400 bronze
Cast bronze
Bronze (C22000 per listing)
Ball
Stainless steel
Polymer
Hard chromed
Seats
PTFE
Polymer
Not stated
Handle
Square hole takes a ratchet
Bronze, easily removed
Stainless, vinyl coated
Bronze is the traditional seacock body because it holds up below the waterline. The ball is where these three differ most. A brass ball depends on its chrome plating; once that wears, the brass underneath can lose zinc in salt water and turn weak and pink. Stainless and polymer balls don’t have that failure, which is why the score has a check for it.
Repair parts for the 1 in. size
Part
Groco BV-1000
Perko 0835006PLB
Buck Algonquin
Ball
BV-1004
In kit 080500699B
Not listed
Seats
BV-1006 (two)
In kit 080500699B
Not listed
Stem or driver
Driver BV-1001-A
Stem 080500699C
Not listed
Handle
BV-1008
080500699D
BBVKIT100LP
Drain plug
1827HB (two)
Not listed separately
Not listed
Perko’s repair sheet gives the order: take off the top hex nut, then the handle and gland nut, ease the stem out of the ball, and lift the ball and seats out the top.
A new lower seat goes in flat side down, the ball with its slot showing, then the upper seat cupped side to the ball. Tighten the top nut while working the handle until it moves smoothly and doesn’t drip.
Questions people ask
What is the best seacock?
On our spec score, the Groco BV-1000 (10.0), then the Perko 0835006PLB (8.6).
What is a seacock?
A flanged valve fastened to the hull that shuts off water coming through a thru-hull fitting.
Can I use a ball valve as a seacock?
Groco doesn’t recommend it: an in-line valve isn’t fastened to the hull, and its NPT threads don’t match an NPS thru-hull.
Is a seacock open when the handle is in line?
Yes. Groco says open is parallel to the thru-hull and closed is perpendicular.
What threads does a seacock have?
NPS at the bottom for the thru-hull and NPT at the top for the hose fitting.
How often should I open and close a seacock?
Groco says at least once a month.
Do bronze seacocks need to be bonded?
Groco and Perko both provide a bonding screw and point to ABYC bonding standards.
What size seacock do I need?
Match the hose size; Perko sizes its seacocks pipe-to-hose at the same size.
Can you rebuild a seacock?
Yes. Groco’s BV rebuilds in place; Perko sells repair kit 080500699B for the 1 in. size.
Should I winterize a seacock?
Yes. Close it and remove the drain plugs so water can’t freeze inside.
How I picked these
Why trust me
I’m Isaac Daniels, a licensed journeyman plumber in Georgia (license #JP507711), and I’ve used all three picks. Every figure comes from Groco, Perko and Hydrasearch documents read Oct 24, 2026, listed below.
How I pick
Flanged bronze ball seacocks only, all 1 in.
Genuine maker listings, new and in stock on Amazon on the day of the update.
Every pick scores 7.0 or more on the spec score below.
Prices come from Amazon’s API with the time they were read.
The spec score, check by check
The seven seacock checks below each count for one seventh of the score. A seacock passes a check only when its maker’s own document says so. Points are added and scaled to 10, to one decimal. No bench test, no customer reviews.
Check (weight)
How it’s scored
Full flow stated (1/7)
Pass if the maker says full flow
Drain plug, 1 in. size (1/7)
Pass if the maker shows a drain plug for the series or the 1 in. size. Where the maker’s own text limits drain plugs to 1-1/4 in. and up, pass only if a 1 in. parts list shows one
Bonding attachment (1/7)
Pass if a bonding or grounding screw is listed
UL listing stated (1/7)
Pass if the maker shows a UL listing for the model
Dimensions published (1/7)
Pass if flange or bolt pattern, bolt size and weight are published
Ball can’t dezincify (1/7)
Pass for a stainless steel or polymer ball
Repair parts published (1/7)
Pass if the maker lists any replacement part for the 1 in. size, a handle kit included
Total
Passes ÷ 7 × 10, to one decimal
Seacock
Flow
Drain
Bond
UL
Dims
Ball
Parts
Score
Groco BV-1000
Pass
Pass
Pass
Pass
Pass
Pass
Pass
10.0
Perko 0835
Fail
Pass
Pass
Pass
Pass
Pass
Pass
8.6
Buck Algonquin
Pass
Pass
Pass
Fail
Pass
Fail
Pass
7.1
Sources
Groco (Gross Mechanical Laboratories), BV Series Full Flow Seacocks info sheet with parts list, 151113.
Groco, FBV Series Full-Flow Seacocks info sheet, 151113; BV and FBV product pages, groco.net, read Oct 24, 2026.
Groco, Valves and Thru-Hull Fittings Installation technical bulletin.
Perko, Seacock Ball Valve Design, Fig. 0835 and Fig. 0805 catalog pages, perko.com, read Oct 24, 2026.
Perko, Cat. Nos. 0805, 0834, 0835 Series Seacocks installation sheet (0805INS1) and repair kit instructions (0805INS2).
Hydrasearch, Recreational Catalog 621, Valves: Ball Type Seacocks (Buck Algonquin).
Amazon product data for B00FFDE0YY, B0851H7X8Q, B002IV8COA, B000Y85KNK, B0CWVP686W, B002IZJ9XY and B000FP0988, read through the Creators API on Oct 24, 2026.
