peterson 35 sailboat

Sailing Whimsy

Adventures on a classic Pearson 35 sailboat

Monday, September 5, 2022

Installing a dorade box vent on my sailboat.

Adequate ventilation inside a sailboat's cabin is a must, whether in the hot tropics or colder climates where condensation becomes a problem. Being stuck inside a hot damp boat interior with no fresh air circulation is a miserable experience especially on passage, or even on a rainy day at anchor, when opening the portlights or top hatches is not an option. 

Whimsy will have 8 opening portlights (7 on cabin sides and an aft-facing one over the galley sink) but because boats tend to point into the wind, cabin-side opening portlights are generally not as effective in promoting air flow. A forward-facing portlight is also not an option as the force of waves crashing over the bow can possibly stove-in the area, not to mention the leaks. The solution is a Dorade box vent.

 Dorade vents are named after the Olin Stephens-designed sea-racing yacht  Dorade  built in 1929 when the Robber-Barons took up pleasure sailing, which is surprising because it seems like such a simple solution to a common problem that should have been invented much earlier: how to get air ventilation below deck without letting water in too.

A Dorade box vent basically consists of a rotating cowl that can be pointed into the wind, attached on top of a teak box that has an internal baffle,  which is placed over a hole on deck. The idea is that the internal baffle will keep out most of the sea spray and rain, which drains out from the bottom of the box, while the air moves over the baffle, down the hole & into the cabin. 

Getting air into the cabin is part of the deal; there also has to be adequate air exhaust routes for proper ventilation to occur. A Dorade box cowl can be pointed away from the wind too, creating negative pressure that will tend to suck air out of the cabin. This is why larger boats can have pairs of Dorade box vents: one facing fore and one facing aft, creating a continuous draft through the boat interior. 

Whimsy doesn't have the deck space for two vents and won't need one because the companionway as well as the yet-to-be installed aft-facing opening portlight over the galley sink, will provide enough of a passive air exit. They will in turn be protected from rain and spray by the yet-to-be installed dodger.

Parts for this project consisted of an off-the-shelf teak Dorade box, a cowl whose base just barely fit over the box, and a ring cut off of 5"wide PVC pipe.

The cowl is the most problematic part. One of the issues with Dorade box vents, other than their primary drawback which is taking up large tracts of deck space, is that the cowl can be a nuisance, fouling lines and banging shins. Traditional Dorade box cowls are fancy highly polished, hard metal objects with sharp edges that look pretty but a jibsheet caught around a Dorade box cowl can potentially rip it right off, and I'd hate to trip onto a cowl. Traditionally the solution was to build a steel cage around the vent to prevent all that, thus taking up yet ore space and not reducing trip hazards. 

Manufacturers came up with PVC cowls that are flexible enough not to foul lines and to not cut you open if you should fall on then, but the general consensus is that they don't fare well under the sun and also tend to stain, turn yellow or mildew. Vetus however has come up with soft but rigid cowls made of silicon, which supposedly fares better than PVC under the sun. I guess we'll see but the material doesn't feel floppy as I had feared.  Anyway I got the biggest cowl I could find to maximize airflow: the Vetus  Samoen  cowl with a gaping air scoop painted red and 5"-wide opening hole on the base. 

The installation of my Dorade box vent was pretty straight-forward as there aren't too many places to install one on deck. I was most concerned with making sure it did not interfere with any lines running aft to the cockpit. Then, installation was simply a matter of cutting a 5" hole on deck, and a slightly larger hole from below (for the cover plate). I went through the usual process of scooping out the balsa core material and filling the gap with epoxy filler. I had cut off about  2" length off of a 5"-wide PVC pipe to make a plastic ring; this was installed over the deck hole with about a 1" tall lip sticking up, acting as a dam to further limit water intrusion around the deck hole. Then a few coats of gel coat, and the quickly "varnished" teak box was stuck on the deck top with 3M 5200 only (I don't see any reason why it would need to be more securely fastened on deck, and additional fasteners just mean more holes for water penetration.) 

To close up the Dorade box vent from below, a 5" (internal diameter) waterproof plastic deck plate was installed from the interior under the hole. 

I decided to varnish the teak box. Though teak tends to be naturally weather resistant, I was concerned as the boards used to make my Dorade box were kinda thin, and so could use protection. I also like the glossy look of varnished wood. The quick-and-dirty varnish job was just two coats of epoxy (first one was Totalboat "penetrating" epoxy, as teak tends to be oily & not stick well to epoxy resin) followed by two coats of Interlux Perfection Plus to give it a glossy look, as well as to protect the epoxy from the Sun's UV.  The final coat was a spray of glossy acrylic from a can with additional UV inhibitors; not strictly necessary but helped deepen the gloss.. Of course there are drips and dust specks galore; I am working in a dusty boatyard. 

So, now Whimsy has pretty much maxed-out the natural ventilation options. Combined with multiple fans, there is not much else that can be done to improve ventilation below, but for a small screen on the cowl to keep out bugs.

Friday, May 6, 2022

Filling-in the bilge sump; restoring engine bay and area below cockpit.

Thursday, January 6, 2022

Marine diesel engine rebuild, part 1: removing propeller and shaft.

WHIMSY came with a Beta Marine 28 diesel engine built in Sept 2000. This is a marinized version of the Kubota BD 1005, meaning among other things that it is cooled by a seawater heat exchanger rather than with a radiator and fan like in a car. They've also added a convenient handpump to make oil changes easier, but mine has been dangling in a wet bilge apparently and has rusted bits that will need replacing. The engine paint is chipped off, there are bits of corrosion and rust, etc.  However, despite cosmetics, diesel engines in general are tough, and will run forever as long as they get regular TLC in the form of clean fuel, regular oil changes and plenty of ventilation. 

Though I discovered the anode zinc pencil on the heat exchanger had been eaten away to a nub, suggesting poor maintenance and additional possible damage to the heat exchanger, the engine ran fine when I had the first test sail back when I first bought the boat. It has been sitting around since then, gathering dust. I can turn the prop shaft in both directions easily so I don't expect it is siezed. I needed to pull it for a rebuild, including head gasket change, and to make improvements (larger capacity alternator, for example, to handle charging a large lithium LiFePO battery bank) 

I wanted to get access to the bilge area and the area under the cockpit too. I plan to generally clean, fill-in the areas of the bilge that are inaccessible by hand (under the prop shaft log in particular) and paint the entire area with white gel coat followed by anti mildew paint on the upper areas (as in the anchor locker, which also tends to be a dark humid environment.) While the engine is out, I plan to reroute bilge drain hoses, install the autopilot, etc. The galley sink drain standing pipe is an open question, I may just glass-in and brace the drain standing pipe more securely, or seal it up and reroute the galley sink drain through a sump pump arrangement overboard above the waterline? I am tending towards the latter for safety though it will be more inconvenient to clean out a sump pump of bits of food and grease.

I also need to repack the prop shaft stuffing box. I had considered a watertight shaft seal but I think this many-hundred year old solution to having a rotating shaft through a hole underwater without leaks, is a pretty good one as it is, even though there will be a constant drip from the stuffing box. Maybe I'll find some way to direct the drip into a the sink sump I was thinking of building...

So anyway, the first thing to do is to remove the propeller, to be able to further disconnect the prop shaft from the engine transmission box. After removing the prop nuts, my prop just popped off easily using a gear puller, no drama no fuss. I just had to push the rudder hard to starboard to get the prop entirely off the prop shaft. The prop shaft zinc anode is new, and I had the cutlass bearing changed already.

Checking the prop, it has some minor nicks but seems fine. I noticed it had a nylon bushing, so it was probably designed for a 1" shaft, while WHIMSY has a 7/8" prop shaft. The bushing may be responsible for the wear on the prop shaft key, so I guess I am buying a new propeller and saving this one as a backup. This is a three bladed 12" diameter bronze prop, so we're talking about $500 new. (Have to figure out the old prop pitch.)

The prop shaft coupling unscrewed easily, though it looks very rusted. It includes an R&D flexible coupler to take-up torsion forces. Ideally I'd like to install a thrust bearing and cv joint (but I don't think there is enough room left over along the drive train that would allow me to also service the stuffing box.) As it is, the forward force of the engine is transfered to the hull via the engine mounts, which is not ideal; a thrust bearing would remove that force off the engine mounts, and the cv joint would resolve alignment issues. (When installing marine diesel engines,  you're supposed to make sure the the prop shaft coupling is aligned to the transmission correctly, checking with feeler gauges, but there is now way to check alignment once the engine is operating. CV joints actually require a little misalignment. )

Once the coupling was unbolted, it was easy to just pull the prop shaft from inside the engine compartment. I had made sure there were no bolts or keys on the other end of the shaft before just sliding it out of the stuffing box. 

The prop shaft seems fine, there is no corrosion, no groves, etc.and no indications that it was rubbing inside the shaft log due to misalignment Prop shafts often are subject to electrolytic corrosion due to stray current, or crevice corrosion esp. in areas along the stuffing box, where the packing deprives the steel of oxygen. The problem is that what may seem like surface discoloration can be evidence of very deep and so invisible corrosion on a prop shaft. Mine thankfully had no issues though I was surprised how short my prop shaft was, about 3 feet. 

Anyway, because I had pulled the prop shaft from inside the boat, there was no need for me to remove the coupling itself off the shaft. This was a relief because with the very rusted set screws on the coupling, I could tell this was a job for a professional machine shop (that will probably end up cutting off the coupling: if you do this, make sure to cut the coupling over the shaft key, to protect the prop shaft itself in case you cut too deeply, then use metal wedges to loosen the coupling off the shaft. If you do manage to get the coupling off easily by just undoing the set screws and using a coupling removal tool (or maybe you have a split shaft coupling, which consists of two parts bolted together over the prop shaft which can be removed much more easily) note it is generally a good idea to not reuse old couplings since they may be warped. Installing a new coupling on a prop shaft should also be done at a professional machine shop to make sure it is mounted square to the shaft. If the coupling itself is warped or misaligned, then the prop shaft and engine will never be aligned right, resulting in excessive transmission and prop shaft wear, maybe even a permanently damaged prop shaft or engine. A new one-piece coupling is about $70.

Saturday, December 18, 2021

Installing the windlass and spurling pipe.

I went with a Lewmar H2 windlass with a gypsy and capstan combination. There are many pros and cons for vertical or horizontal windlasses as well as as above deck and below deck ones. Horizontal, above-deck windlasses are just easier to deal with as far as I am concerned. It is a pretty substantial piece of gear, both in terms of size and weight. It can pull at least 1000 lbs, so it should be able to handle the weight of my Rocna Vulcan 40 kg anchor and 250 ft. of chain (just about 300lbs including the swivel.) My complaint about the Lewmar H2 is the cost of additional "optional" manual re kit, over, which is actually pretty much necessary so add on another $500 or so to the cost. 

The location of the windlass installation was a bit of a problem because cause Whimsy has a teak anchor roller platform which extends aft from the bow for about 2ft, then there's a few inches of space followed by about another 2 ft. of space taken by the new anchor locker lids. So the windlass is mounted about just about 4 ft from the bow, aft of the anchor locker. This meant I had to split the anchor locker lid into two opening parts, in order to allow it to open with the anchor chain passing above it. I actually prefer this arrangement over having a one-piece lid which would be bulkier. 

The windlass is therefore located on the foredeck about 4 ft from the bow, which puts it over the v-berth in the forecasle area which is particularly prone to leaks (the foredeck a boat is pretty wet when sailing, as waves break over the bow with great force.) Since a soggy v-berth mattress is about the worse thing there is to sleep on, I would have preferred not to install anything over this part of the foredeck at all,  but choice have to be made (locating a heavy piece of gear further aft has advantages in better sailing performance too.) I am just going to have to live with deck penetrations for the bow cleats and windlass over the v-berth and do my best to make sure they're installed well so they won't ever leak!  

So aside from the leak issue, there was the question of how to get the anchor chain to feed into the anchor locker, which is separated from the v-berth with a bulkhead. There used to be a little hatchway in the bulkhead to allow access to the anchor locker from below, but I sealed that up when I cut a new anchor locker opening on the decktop instead. 

My solution was to make a spurling pipe  (not to be confused with a hawse pipe) shaped with a gentle curve that feeds the chain from the windless on deck, down past the v-berth interior space, past the bulkhead and into the anchor locker. 

Designing the spurling pipe and its installation took some doing, as there are many variables. For example Lewmar recommends at least 1 foot of drop from the windlass for the anchor chain to be able to self-feed under its own weight, and yet I also had to make sure the outlet of the spurling pipe was high enough in the anchor locker to prevent the chain from castling. A few dry runs with the old anchor chain showed that it chain slides through the stainless steel pipe, and a gentle curve starting from about 8"that terminates about 1 ft from under the windlass, proivded enough drop for the chain to fall through the pipe easily under its own weight. This location also provides another 2 feet or so of vertical drop inside the anchor locker, which should be adequate to prevent the chain from piling up too much. 

The spurling pipe is made from heavy-gauge 316 stainless steel, with a 2" diameter. It has a has an approx 5" flange plate that I had welded on, that secures it to the bulkhead with 4x 11/2" bolts through the bulkhead. I had a tab welded (badly) on the pipe lip on decktop after installation, thus securing it from both ends. On decktop, the spurling pipe lip is located just under the windlass gypsy so the chain falls into it neatly. In the anchor locker, I placed a roller in front of the pipe opening, so the chain can easily slide in and out of the spurling pipe with minimal wear and noise. (I made a curved part from aluminum, used to make sure the chain doesn't jump out of the roller.) I painted it with anticorrosion paint though technically stainless steel doesn't need it; exposure to air is what keeps it rust-resistant.

Others have used PVC pipe for similar spurling pipe arrangements but it seems to me that steel chain (covered with bottom sand too) will quickly wear through PVC. Also, some have arranged for the spurling pipe to feed into the locker underneath the v-berth rather than into the chain locker, this moving the anchor chain weight farther back. I decided against this because I didn't want to lose the foot space in the v-berth and I have other plans for the storage area under the v-berth. I plan to move the chain even further back into the bilge in preparation for long transits anyway. 

Lewmar requires the H2 windlass to be lined-up just right with the anchor chain, so I had to make a platform or plinth to raise the windlass about 2 inches from the decktop to line it up vertically with the teak anchor platform and the anchor rollers. I decided to make this plinth out of teak, for looks, but I found a 2"-thick cutting board on Amazon.com for less than the price of buying the raw teak. All I had to do was trim it to shape, and seal it up well against the elements. For this, I followed the same procedure as for the teak anchor platform: First, two or three coats of West epoxy with their special clear part B, followed by several coats of Perfection Plus clear gloss varnish (5? enough to create a glass-like surface effect; this is helped by using a heat gun on low setting to blow out bubbles that inevitably form when varnishing.) Though the varnish is supposed to have UV-resistance, this was then covered with 3 coats of sprayed-on Nyalic clear coat, resulting in a tough, UV-resilient and deep clear gloss surface on the windlass plinth (as with the anchor platform.) But before the plinth could be installed, I glassed-in a solid plate of G10 fiberglass, to account for the camber of the decktop. The teak plinth sits on top of this plate. 

The Lewmar H2 windlass requires 4x12mm bolts to secure it in place. They helpfully provide the bolts and nylon lock nuts (along with a pre-cut rubber gasket seal to fit under the apparatus) however the bolts were too short for my installation especially due to the 2" thick teak plinth that the bolts would have to pass though, so I had to order some 12mm threaded rod of 316 stainless steel to cut-up my own custom length bolts.  I had to calculate the length of the bolts to make them long enough to fit into the windlass housing body for about 1", then through the plinth and the decktop, then past the filler & backing plate for the windlass below, followed by enough threads to use a washer and locking nut on them ... or about 6" (including a little extra to account for the butyl sealant.)  

The backing plate was made from 5/16 aluminum diamond plate. I got it for free, it easier to cut than steel, and it seems plenty strong enough to secure the windlass. Normally I would not use aluminum backing plates as steel bolts in combination with aluminum will result in galvanic corrosion, but this installation was in the dry interior of the boat so corrosion is much less of a concern. I used nylon washer spacers just in case though. Since the steel bolts were inserted into the aluminum body of the windlass, I made sure their ends were well-covered with generous goops of Duralac anti-corrosion compound. 

I also used gob of fiberglass filler when installing the backing plate to flatten out the reverse camber of the interior roof of the forecastle, under the windlass installation area, so the strain from the windlass is distributed as evenly as possible under the deck.

Wednesday, September 8, 2021

Building new stairs

Wednesday, December 11, 2019

Investigating the rudder shoe.

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