Thursday, May 1, 2014

Inflatable Dinghy & Outboard - Part 1

--Blog post written by Bob

While cruising the Bahamas in just a couple years, our dinghy will be our primary transportation to/from land, to/from snorkeling spots, and for most local exploration.  It is the equivalent of a car (or pick up truck) for land dwellers--so, it is an important acquisition.


An example of a Rigid Hull Inflatable Boat

While making open water passages (like crossing the gulf stream) or traveling along the Intra Coastal Waterway, the outboard engine will be stored on the stern pulpit and the dinghy will be stored upside down on the foredeck.  We will have a mechanical lift to raise the outboard motor from the dinghy (when in the water) to the boat's stern pulpit--this lift has a mechanical advantage of 7-to-1.  We will use the secondary jib halyard (a recent addition described in our blog post dated March 9, 2014) for lifting the dinghy onto the foredeck.  Both of these lifting operations will require Maggie and I to work together--neither is a one-person job.

Incidentally, when I cruised the Bahamas previously, we had an 8-foot long hard dinghy and a 2 HP Johnson outboard motor. It was fine for getting from the marina to our mooring but it certainly wasn't the best choice for the Bahamas.

Dinghy Selection Criteria

Having owned an APEX 10-foot RIB (weighing 149 lbs) with a 15-horsepower 2-cycle outboard (weighing about 80 lbs) for over 10 years, I have some experience in this area.  I like the performance of a RIB (rigid hull inflatable boat).  However, I want everything to be lighter in weight this time around.  With the new 4-cycle outboards, outboards are now heavier for a given horsepower rating.  For ease of lifting, I prefer that the RIB weighs under 100 pounds and the engine weighs under 90 pounds--the latter is important because I have to lift it manually for servicing once a year.

A RIB is an inflatable boat with a rigid hull--the structure between the inflated tubes.  PVC is the least expensive material for the tubes but it doesn't last long enough in the tropical sun.  Since I am only considering tubes constructed from Hypalon, I have narrowed the field down to the following four alternatives which meet my weight criteria:

Table of Dinghy Alternatives Being Considered

I have personally looked at each brand of dinghy and made notes on features I liked and disliked.


Based on weight, AB's aluminum hull is really attractive--the 9-foot long model only weighs 75 lbs!  However, this weight benefit is barely noticeable on the 10-foot model, weighing 95 lbs.

Despite being only 1/8-inch thick, the aluminum hull seems very stiff and durable.  The only downside  of an aluminum hull is the fact that if it is ruptured in service it would require a repair by welding.

AB has always had a reputation for a smooth and dry ride because of their hull shape having a deep V and a high bow. However, one of the things I didn't particularly like about AB's Ultra Light models is that the hull design has a shallower V than their regular line and the bow is not as high.

The cost of an aluminum hull AB RIB is higher than the equivalent-sized fiberglass hull APEX RIB.


APEX's fiberglass hulls are slightly heavier than AB's aluminum hulls.  At the 9-foot length, the difference in weight in 20 pounds but at the 10-foot length the difference is only 4 pounds.

One of the things I liked about the APEX Lite line is that the hull is identical to their regular line (which I am very familiar with)--they simply removed the flat floor from the design to make the Lite models.  So, they will ride very smooth and dry.

The fiberglass hull of the APEX RIB is very flexible when you step into it.  Based solely on observation, APEX's fiberglass hull would be more likely to rupture than AB's aluminum hull (if you hit something in the water while traveling at high speed).  If the fiberglass hull is ruptured, I could make a fiberglass repair as needed almost anywhere.

In the end we decided to buy the APEX 10 Lite but AB's 10 UL was a very close second.  APEX's lower price and the excellent service provided by Fawcett's Boat Supplies made the difference.

Smart Tabs

Jesse Tucker at Fawcetts highly recommended the use of Smart Tabs (manufactured by Nauticus).  Smart Tabs are small flaps that are mounted on the stern of the dinghy near the waterline.  They are held downward by a small pneumatic cylinder with fixed air pressure.  As the boat begins to move forward, the tabs are down in the water.  The force of the moving water against the tabs forces the stern slightly upward--this makes the dinghy plane faster.  As the boat begins to plane, there is enough water pressure against the tabs to keep them parallel with the hull--this essentially increases the waterline length and requires less power from the outboard motor to maintain the plane.  Through the use of Smart Tabs we can safely reduce the engine size for our dinghy.

Smart Tabs Manufactured by Nauticus

Outboard Motor

All my previous outboards have been made by Johnson/Evinrude.  I really like Honda and Yamaha because they are quieter than others and have an excellent reputation for dependability.  Because the Yamaha is lighter than the Honda in this size range (6 to 10 HP), has a reputation for service available anywhere in the world, and the fact that I've had good experience with a Yamaha scooter, I'm going with a Yamaha-brand outboard engine.   I realize that a big part of this decision is personal preference.  The following three alternatives meet my weight criteria:

Table of Outboard Motors Being Considered

Having decided on the APEX 10 Lite dinghy with Smart Tabs, we opted for the 8 HP Yamaha outboard. This seemed like the best compromise between weight, power, and cost.

Ethanol-free Gasoline

Having been through a myriad of problems with ethanol in gasoline with my previous 15-horsepower outboard, I plan to use only ethanol-free gasoline.  Ethanol-free gasoline is rarely available (and at a higher price) locally but readily available in the Bahamas.

Bow Bag

Having used a custom-designed bow bag on my old APEX dinghy, we intend to use a similar design for our new dinghy.  The bow bag will hold two life preservers, a small anchor, extra spark plugs, and a few tools.

Writing this blog post allowed me to carefully consider all the elements involved in this decision.  I hope it all works out like I expect.  I will report back on the results at the beginning of July.

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