CASE STUDY 2: BUILD­ING A UNIT FROM SCRATCH

SAIL - - Boat Works - —Brian Flana­gan

When we de­cided to re­fit our 38ft sail­boat for full-time cruis­ing, my wife, Tara, in­sisted that we add pres­sur­ized hot wa­ter, a cabin heater and a re­frig­er­a­tion/freezer sys­tem. The first two I felt com­fort­able in­stalling, but I had no ex­pe­ri­ence with marine re­frig­er­a­tion and had read enough ar­ti­cles on the sub­ject to know that there is no sin­gle right way to go about in­stalling such a sys­tem on a boat. Re­frig­er­a­tion is one of the top en­ergy draws on a small boat, and I did not want to get this wrong.

The first thing we had to de­cide was whether to in­stall a self-con­tained pre-made unit or build our own re­frig­er­a­tor/freezer box. Af­ter tak­ing mea­sure­ments where we wanted the sys­tem to go, we de­cided build­ing our own box would make the most ef­fi­cient use of the space. Once that de­ci­sion was made, we now had to find the best 12-volt re­frig­er­a­tion com­po­nents for our needs. Much on­line re­search en­sued.

We soon zoomed in on the Sea Frost BD sys­tem. Owner Cleve Hor­ton be­came an in­valu­able re­source while we built the box, help­ing to de­ter­mine the di­men­sions and amount of in­su­la­tion to make the sys­tem as ef­fi­cient as pos­si­ble. We chose the BD sys­tem be­cause it would be suf­fi­cient for our box size and can be air cooled. Wa­ter cool­ing is more ef­fi­cient than air cool­ing, but if the box is well in­su­lated and not too large, the dif­fer­ence in ef­fi­ciency is not large and air cool­ing sim­pli­fies the sys­tem and low­ers main­te­nance.

In ad­di­tion to the ba­sic BD sys­tem, we chose a freezer bin and an elec­tronic ther­mo­stat with com­pres­sor speed con­trol op­tions. The freezer bin con­sists of two di­rect evap­o­ra­tor cold plates set on op­pos­ing sides of the bin, cre­at­ing a small freezer. The rest of the box be­comes the re­frig­er­a­tor as cold air spills over from the freezer bin. The elec­tronic con­troller al­lows us to set dif­fer­ent com­pres­sor speeds for when we are in dif­fer­ent cli­mates. It also al­lows us to mon­i­tor re­frig­er­a­tor tem­per­a­tures as well as cold plate tem­per­a­tures, which makes it easy to ad­just plate tem­per­a­ture for a de­sired re­frig­er­a­tor tem­per­a­ture.

The hard­est part of the job was build­ing the box and then de­cid­ing where in the boat all the other com­po­nents would go. This needed to be done so Cleve would know how long to make the coolant lines and wiring har­nesses. We had enough room

3 to build a 4.4ft top-load­ing box, which would al­low us to use 6in of Dupont TUFF-r in­su­la­tion around all four sides and bot­tom. We used 4in of the same ma­te­rial for the top and hatch doors. This would give us an “R” value of 39 on the sides and bot­tom and 26 on the top. The freezer bin set in the back of the box would be just un­der one cu­bic foot. This sounds small, but it has worked well for us liv­ing aboard full-time.

I used marine ply­wood to form the box and laid four lay­ers of fiber­glass cloth on the in­side, wet­ted out with WEST Sys­tem epoxy resin. As I did this, I also mixed a white dye with the epoxy so the in­side of box would not need to be painted. It is crit­i­cal to make the box wa­ter­proof to keep mois­ture from get­ting to the in­su­la­tion and keep out any air cir­cu­lat­ing out­side the box. Next step was build­ing mock­ups of the freezer bin and com­pres­sor/con­denser box. Af­ter I had the three ma­jor com­po­nents of the sys­tem, the box and mock­ups, I cut the in­su­la­tion and

set ev­ery­thing in place, so I could make the re­quired mea­sure­ments for Cleve.

Af­ter re­ceiv­ing the me­chan­i­cal com­po­nents from Sea Frost, it was just a mat­ter of putting all the parts to­gether. The whole sys­tem came fully charged with re­frig­er­ant; the coolant lines be­tween com­pres­sor and evap­o­ra­tor plates also re­main sealed un­til the con­nec­tors are torqued to­gether, so as­sem­bly was easy.

It took a few days of ad­just­ing the ther­mo­stat to get the re­frig­er­a­tor com­part­ment to our de­sired tem­per­a­ture, but once we got a feel for the con­troller and a base­line of cold-plate tem­per­a­tures it be­came a sim­ple pro­ce­dure. We have found no need for a cir­cu­la­tor fan in­side the box. Power draw varies, but the max­i­mum is ap­prox­i­mately 40 Ah per day.

This re­frig­er­a­tion unit is sim­ple and has run con­tin­u­ally for al­most three years with­out a hic­cup. The only up­keep is de­frost­ing the freezer based on the hu­mid­ity and ice build-up, about once a month. But at the end of the day, we al­ways have ice for our sun­down­ers!

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