Pearson 30 questions...any answers?

[rockhopper]

Let's summon him back over, I'd like to put my boat back in the water. Was just curious if 1/2" would be fine or if going to a 5/8 would be more trouble than it was worth if you had to expand the hole.

Pearson did a wonderful job on the external hull to deck flange, there's a couple of spots where the hull is almost flush with the edge of the deck. Is this to be concerned with? I don't foresee being able to get it pushed back in.

[sastanley]

I sent him an e-mail. On my boat, I have a 1/2" thru-hull connected to a 5/8" hose for the engine intake. It seems to work fine, but the restriction is definitely the I.D. of the 1/2" thru-hull/1/2" marelon seacock/hose barb.

The amount of cooling can also depend on how you have things set up. I've known this about for about 40 years, and it ran 150-165°F when it was raw-water cooled for 35 years. About 4-5 years ago when I installed a HX and went to antifreeze cooling, the temperature went up to about 165-175°F for the same cruising RPM. A zillion factors can affect this (size of HX, size of hoses, the smallest fitting is always the choke point, etc.) -

One other thing I did which increased raw water side flow volume was a Moyer 502 pump that replaced a once rebuilt Oberdorfer 202m3. The difference in flow out the transom was definitely noticeable, so the ol' Oberdorfer pump was not quite getting maximum flow possible thru the thru-hull.

[Oldlaxer1]

Let's summon him back over, I'd like to put my boat back in the water. Was just curious if 1/2" would be fine or if going to a 5/8 would be more trouble than it was worth if you had to expand the hole.

I'll ask him to jump back in. He's pretty active on Sailnet

[Administrator]

I haven't run the numbers, but I'd bet a set of plugs that, at the flow rates at work here, the pressure drop across a 2 or 3-inch length of pipe at a diameter of 0.50 inches isn't meaningfully different than if the diameter were 0.625 inches. Higher loss, yes. Meaningful, no.

Any takers? (one winner only )

Bill

edit: The "not meaningful" refers to the MMI or Oberdorfer pumps. With electric pumps, EVERYTHING is meaningful.

[ndutton]

I upped from a 1/2" external grate thru-hull to a 3/4" open type (added a raw water strainer at the same time) for a completely different reason. The larger open thru-hull gave enough internal room to brush bottom paint up inside. Growth was an issue with the smaller one and the combination of size and grate made it impossible to prevent.

Edit:
Bill, increasing from 1/2" to 5/8" thru-hull (???, I've never seen that size before but whatever) ups the cross sectional area 150%. Go to 3/4" and it's 225%. The limiting factor I think is the Oberdorfer pump inlet and outlet @ 3/8". It's interesting too that there is no difference in Oberdorfer's capacity specification between 3/8" and 1/2" ports.

[Ajax]

I'm here, I'm here.

Shawn, yes we did up-size my raw water through-hull from something like 1/2 to 3/4". This also eliminated a 90 degree elbow that would slow down water flow. We used Marelon.

We eliminated the external grating because it would just foul and impede waterflow. This worked fine and I had no issues with that setup. I did eventually clean out my cooling jacket et al, when exhaust flow dropped.

The OP has those damned rubber cone Groco seacocks. Lube the rubber body with Marelube. It's safe and won't attack the rubber. Do NOT operate the valve without first releasing the T-handle on the side. It is normal for the seacock body to weep around the body fitting while operating the valve, even when the seacock is in perfect condition. Only be concerned if the weeping doesn't stop when you snug up the t-handle.

Hope this helps.

[rockhopper]

So the question is do I leave the hole alone and install a 1/2" or make the hole bigger for a 3/4" thruhull. At 3/4" why'd you go with the Marelon? I think I'd read the barnicals didn't attach to the Marelon and you didn't have to worry about corrosion, if that's the case then it'd be worth it.

Did you use a backing plate? All the backing plate I've seen only go down to 3/4" thruhull.

[sastanley]

RH..I made my own backing plates..I used either 1/2" plywood saturated with epoxy, or PVC board depending on the particular application..i.e., how thick was the hull and how much thickness did I need on the inside to snug down the seacock without bottoming out on the thru-hull threads. I 5200'd and clamped the backing plates to the hull while the 5200 cured, and then I used short sheet metal screws to attach the seacock.

In all honesty, I personally think the threads on the thru-hull itself are plenty strong enough..dunno if that follows all ABYC/USCG standards though, if they exist. At least the sheet metal screws into the backing plate keep the seacock from accidentally backing off the fitting, likely impossible with hoses attached anyway. If the gobs of 5200 I used ever fail, I have bigger issues and I am in REAL trouble!

[rockhopper]

Tac, your water lift muffler appears to be on the port side with the fuel shutoff, mine was on the starboard side screwed on to a shelf part way up the fiberglass and the exhaust ran through a hole in a board at the aft. How is your muffler supported and how does your exhaust hose run?

Not sure if it was standard or not but the cockpit locker on the starboard side has pegboard which the exhaust had to go around.

Sastantley, 5200 takes 7 days to cure fully doesn't it or how long did you let it cure? Did you just paint epoxy on the plywood? Sorry for 15 million questions, just don't want to sink. Don't think I've ever seen PVC board.

[sastanley]

I had the boat on the hard for an entire winter, so cure time was not really an issue for me. I did just 'paint' epoxy, but several coats over several days until it stopped soaking in and started building up on the outside (don't forget to drill the hole prior to so this gets epoxy soak too.)

PVC board comes in various sizes and thicknesses..there is an end cap at my local Lowe's that sells half a dozen different sizes like 1" x 4" x 8', 1"x 6" x 8', etc., and a local independent hardware store has some as big as 1"x12"x8', which is really ~3/4" thick. I had scrap around from other projects, and you can probably find shorter pieces, as it is a little pricey compared to wood lumber.

If your boat didn't sink with a gate valve and no backing plate, anything you install will be an improvement!

[roadnsky]

In addition to the excellent links Neil listed in post #19
here is a decent youtube instructional and the attached Don Casey PDF as well.

https://www.youtube.com/watch?v=moxnIBRFbgc

The youtube video shows how to make backing plates.

[ndutton]

I read the Don Casey pdf quickly so maybe I missed it but there are two additional considerations when orienting the seacock:

• Handle swing - place the seacock handle so it's easy to reach and operate and at the same time paying attention to . . . .
• Drain plug - a proper seacock has a valve chamber drain plug. It should be oriented at the lowest point to drain effectively for winterizing

[Van_Isle]

I used marine ply with epoxy coating but bedded them in Sikaflex 291 vs. 3M 5200. I figure the last backing plates lasted a good long time, but at least with Sikaflex, I, or the next owner of the boat, will be able to remove for replacement. Wood also allowed me to easily shape the backing plates to fit hull curvature. I'm just feeling that PVC, like Starboard, would be too flexible to provide much stiffening backing.

I used Groco thru-hulls and valves ... which are a premium over the typical no-name offshore product most typically found. I did not use the flanged adapters that Groco sells, although I might retrofit them for the larger thru-hulls, just for peace of mind. The thru-hulls I used are combination-threads, so this helps with thread mis-match.

One surprise I had (this was all done the 1st time I pulled the boat to do the bottom after purchasing it) was that the original thru-hulls were flush-mount and all the flange of all currently available flush thru-hulls are smaller in diameter than the originals. I had to fill the recesses with epoxy and went to standard mushroom-style thru-hulls. This, along with with removing multiple coats of bottom paint, fixing blisters and other minor hull repairs and applying a barrier coat really ate up the time I had available to do the job. Another reason I didn't use the flanged adapters.

[Ajax]

So the question is do I leave the hole alone and install a 1/2" or make the hole bigger for a 3/4" thruhull. At 3/4" why'd you go with the Marelon? I think I'd read the barnicals didn't attach to the Marelon and you didn't have to worry about corrosion, if that's the case then it'd be worth it.

Did you use a backing plate? All the backing plate I've seen only go down to 3/4" thruhull.

Marelon doesn't corrode, but it's not immune to bottom growth. I've had growth foul enough that I had to remove the raw water hose and ream out the Marelon seacock with baby bottle brush.

[rockhopper]

Okay so the water lift exhaust exit on my 73 Pearson 30 is 2" O.D. hose was 2" I.D., the raw water hole is 3/4".