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Considerations for upgrading our 3.5 hp dinghy motor

Dinghy Motor

Considerations for upgrading our 3.5 hp dinghy motor

In my last post, I wrote a review of our Mercury 3.5Hp outboard motor that we use on our 8′ 2″ inflatable dinghy. We have had this boat and motor since we purchased Calypso 7 years ago. While this combination has served us well, since we now have Calypso II, I have been thinking about making a change. Let me start with the considerations that are leading me to think about a change.

We currently carry the dinghy on Calypso on Weaver davits, tipped up against the transom. To do so, the engine is stored on a custom bracket on the swim platform and must be mounted each time we want to use the boat. These davits work well and were easy to install when we purchased the boat. Mounting the engine each time is not too bad given the light weight of the 3.5 hp motor but still a hassle and requires two people to transfer it between Calypso and the floating inflatable. For Calypso II, we have decided to use arm style davits to carry the dinghy so the engine can stay on the boat all the time. ( see my post on choosing the right davits). As result we could have a boat with a larger heavier motor that does not need to be transferred back and forth.

Other considerations for upgrading is as mentioned in my last post, the 3.5hp only carries 1 quart of gas and needs to be refilled from a jerry can every 45-60 minutes of run time. Lacking a reverse gear, the motor must be pivoted 180 degrees to reverse. At a tight dinghy dock, that does limit maneuverability a bit. For my wife and daughter, who are far less experienced running the boat, this is difficult maneuver. Also, the 3.5 hp on our current 8′ 2″ high pressure floor inflatable will not plane. When carrying four people, in anything other than flat calm water the bow digs in a bit and makes for a wet ride. The dinghy itself being 8′ 2″ and with our typical load of 3-4 people, when you throw in a beach bag, some chairs and the required jerry can, it gets a bit crowded.

So, what are we considering? A step up to address many of the concerns raised would be an aluminum hulled RIB around 10 feet long and powered by a 9.9hp motor. Such a boat would provide more room, range, speed and comfort. It would also be expensive. with an electric start motor, my wife and daughter would be more comfortable operating it. However, a rig like this would be new around $4,500 dollars. Additionally, with the rigid hull, we could not be able to transport and store the boat at home as we do with the current inflatable so that we would incur additional winter storage costs.

An alternative to a full rig upgrade would be purchasing a larger motor for our current boat. If we were to buy a 6 hp motor, which is the largest our current dinghy can handle, we would gain some of the benefits we are seeking. The boat would have an external 3 gallon fuel tank giving it more range. The motor has a full reverse gear. The power upgrade would push the boat faster and raise the bow up so it would not dig in as much and make the ride drier. By only upgrading the motor, we would preserve the ability to store the boat at home and the cost would be substantially less. A new 6hp outboard cost around $1,400 new and used ones can be had for less than that. A further offset would be selling the 3.5hp that we currently have. This upgrade would not improve the space limitation in the boat and it would relay on our current boat which is 7 years old. PVC inflatables, depending on use, can last between 10-15 years at which time seems scan start leaking.

No decision is pending, and we will think more on this idea. Please feel free to comment and suggest what you think is best.

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