Marine Deep Cycle Battery Size Chart

A short while ago I gave a presentation on marne battery and charging systems to a group at a local marina. One item that we discussed was battery groups and sizes and to that end I compiled a chart of the sizes most common to marine applications. I have since been asked to post that information here.

Batteries Size Codes

Group 24       60-85AH     11X7X10”       50-55 lbs

Group 27     85-100AH     13X7X10”       60-65 lbs

Group 29     100-110AH   13X7X10”       65-70 lbs

Group 31   105-115AH     13X7X10”       70-75 lbs

4D             210-225AH       21X9X9”       135-140lbs

8-D           225-255AH     21X11X10”      160-175 lbs

6 Volt GC   200-240AH   10X7X11.5”      60-70 lbs

I would like to add that this information is averaged and that may be accurate to within about 6mm (1/4″) or so on size and that the capacity may be more or less 10%.

Battery size codes Eg: Group 27, 4D etc. refer to the physical size of the battery only and it is not indicitive of the capacity.

You will also note that Groups 29-31 are all listed at the same size. Again some may be slight larger and some slightly smaller.

At the bottom the 6 volt battery is labelled GC. This stands for Golf Cart and being 6 volt, 2 batteries must be wired together in series in order to produce the 12 volts that is commonly required for marine applications. When you compare a 6 volt battery’s space requirements as apposed to their current capacity the advantage becomes very clear. Another note about 6 volt batteries, that is if you’re considering going this route is that while they have a slightly smaller size foot print and they are taller than their 12 volt counterparts and this needs to be considered in the planning.



Fiberglass Boat Construction Part 3 Cores

Back to our discussion of fiberglass boat construction. Last time we looked at the various materials used in cored hull and deck construction. We learned that the most common materials are End Grain Balsa Wood and various types of Closed Cell Foam. The next question is, that since these materials are rigid and do not bend, how do boat builders manage to shape them into the compound curves necessary for hull and deck construction. Core materials are supplied in various configurations other than standard sheets. It can be supplied in narrow strips and small blocks attached to a scrim which is a thin flexible material that hold the blocks together and the small gaps between the blocks, called Kerfs allow the material to be shaped into both single and compound curves. Below is a diagram of core material showing the blocks, scrim and kerfs.

Core Close up1_Layout2

Here we can see a Balsa core material laminated into a boat hull. The kerfs are easily visible between the blocks.

This is a side view diagram of sandwich core construction as used in boat hull.

Cored GRP Hull2_Layout4

When performed correctly sandwich core construction can provide strong light structures but the trick here is to ensure that core materials are installed correctly. As we’ll see in future posts this has been somewhat of a problem for boat builders over the years.

Surveying Fiberglass Boats in Sub-Freezing Temperatures

Every winter I get request to survey boats when the ambient temperatures are below freezing. Surveying fiberglass boats in sub-freezing temperatures just doesn’t work and here’s why.

As we have previously discussed fiberglass as a material is hygroscopic (it absorbs moisture over time) and as such, during the winter months when the ambient temperatures are below freezing any moisture contained in fiberglass structures, such as boat hulls and decks freezes as well. During the freezing process crystallization of the substance occurs, adding small air pockets which make electronic moisture detection virtually impossible. Also because the substance is frozen it becomes very hard rendering percussive sounding tests useless as well. It is for these reasons that I do not recommend surveying of fiberglass boats when the ambient temperatures are below freezing. Any surveyor who claims that their inspections are valid under these circumstances is, in my opinion simply not being truthful and should be seriously questioned.

Solid and Sandwich Core Fiberglass Boat Hull and Deck Construction. Part 2

Now that we have discussed some of the terminology and nomenclature used in fiberglass boat building we can take a closer look at some of the materials. OK, let me get this off my chest right now. I severely dislike the use of the word “OSMOSIS” in any discussion  pertaining to fiberglass boats. It has become one of the most misused generic terms to describe almost any type of moisture related malady related to fiberglass boats. Let me explain further. Webster’s Dictionary describes osmosis as: Movement of a solvent (as water) through a semipermeable membrane (as a fiberglass structure) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane

So taking the above into consideration, in order for Osmosis to occur in a boat hull we would need to have water present on both sides of the hull and in reality we have water only on the outside of the hull (hopefully). In addition, when taking into consideration the thickness of most fiberglass hull structures this should rarely, if ever occur.

What we do see with fiberglass resin is that it does do is exhibit hygroscopic properties, with different resin formulations showing this to varying degrees. Back to Webster’s Dictionary again:

Hygroscopic – readily taking up and retaining moisture. Taking it further, the ability of a substance to attract and hold water molecules from the surrounding environment.

This is what resin can do with the condition sometimes manifesting itself as gel coat blisters and softening of core materials. We’ll talk more on this later.

Next are the Spun Glass Re-enforcements utilized in fiberglass construction. The two most common configurations are:

Glass Matt                                                     Woven Roving

Fiberglass Mat                              Fiberglass Woven Roving

They are usually alternated in layers and saturated with resin to make up the required thickness of the laminate.

Now lets look at the Core Materials utilized in Sandwich Core Construction.

1-Endgrain Balsa Wood: Probably the most common if all the core materials in use today. Its open cell make up gives it good bonding strength will all the resins. It is light in weight and when used correctly it makes strong structures. Balsa has been used almost universally in deck and cabin superstructure construction. It has one serious weakness in that it softens and decomposes rapidly when exposed to moisture. It has however been used successfully for many years and I might add, un-successfully as well.

2-Closed Cell Foam: Foams have been around for some time now and are marketed under various brand names such as Airex, Divinycell, Corecell etc. They are more water resistant than Balsa and due to their closed cell make up bonding strength has been brought into question. They are also light and strong.

3-Plywood: Has seen limited use as a core material. Its tendency to delaminate when used with polyester resin in damp conditions has been an issue and since it is rigid and stiff its use has been somewhat limited to flat surfaces.

Next time we’ll look at core configuration, how it gets formed into compound curves when used in hull layups and the issues that this can cause

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