LZ
07.06.2021 15:52:14
Re: Use Long shaft on dinghy. [links]
See full version: Use Long shaft on dinghy
Re: Use Long shaft on dinghy. [links]
Re: Use Long shaft on dinghy. more
Re: Use Long shaft on dinghy. [links]
I don't know if it is such a big deal on a low performance dink type boat. <br />I had a 4omc longshaft on two 8' dinks and a 10' dink. total time approx 4 yrs (2 cruising & 2 dockside) It was too much power so most of the time they ran at 1/2 throttle. Beaching was the only time I could tell any difference and they manually tilt easy so that didn't bother me either. I still have the 10'r but the 4 was replaced with a 3omc short shaft. here
In addition, the motor will experience less top-end performance and more drag. However, a long shaft length works perfectly fine. You’ll want to stay away from shallow water to prevent hitting the floor. [links]
In addition, you’ll need to measure the transom length, which is the back of the boat where the outboard motor is mounted. more
A shaft length that is too long runs the risk of hitting submerged objects such as rocks or logs and potentially hitting the bottom. [links]
You’ll know that the shaft length is correct when the cavitation plate is in line with the very bottom of the boat. The cavitation plate is the large plate that extends over the prop of your dinghy. here
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For the past few months I have been searching a variety of forums and outlets for a new toy come spring. I had a few RIBs in mind and hadn't given too much thought to inflatables until I came across Saturn's 15 foot model - the SD470 inflatable boat. Its not often stumbles upon a boat with a low transom that is designed for an 15" inch shaft on the motor, let alone one that can be deflated and packed away when I am done. I am an avid spearfisher and I frequently find myself with a need for maximum horsepower once I am outside the marina.
The waters out here on the Pacific coast have some pretty decent current and swells to them so most of the more adventurous boaters who do venture out on them tend to keep their motors performing at peak so having something with a shorter shaft is really ideal for those of us who need the increased maneuverability and handling. I've tried using 20" inch shaft motors - a 40HP I had laying around from a few summers ago and I found that even by raising it a little with a jack plate I still encounter some rough turning at higher speeds plus the drag from all the extra prop being down makes the ride too choppy for my tastes.
I enjoy the excitement of rushing across the swells so to have the motor sit high is a real benefit for me so I
try to leave the prop just deep enough to not blow bubbles and I am cruisin' happily. I've taken control a few times of Seamaxx equipped with a 3" Jack plate and have never been able to achieve the control I
really want to. The boat always feels heavy in the water and really bogged down when the gas is delivered. Many people say that your top end speed will suffer when using a short shaft motor but I inclined not to agree. Perhaps because the boat weighs nearly as much as I do there isn't much slowing me down. Now I am able to be well past the markers before the wife even notices that I am gone!
I currently have a Mercury 5hp long shaft outboard which I use with my permanently beached 10ft GRP tender. I usually leave the tender on my (swinging) mooring when I go sailing and put the 5hp engine on the outboard bracket - so that I have an emergency engine in case of main engine/tiller failure. The 5hp engine is bit heavy to shift around and I would like to get rid of it and buy a lighter 3.5hp long shaft instead. I have an inflatable in a valise on board and would like to be able to use the 3.5hp engine with that too. The long shaft works OK with my GRP tender although it does push the bow up and I have to keep the revs low. A couple of people have told that it's a bad idea to use a long shaft with an inflatable, but I wonder what thoughts folk here might have?
I also wonder whether it might be possible to adapt the transom on the inflatable to take a removeable, slot-in piece of timber which would raise the transom to accomodate the extra shaft length? I've never seen anything like this and I'm surprised that it hasn't been manufactured (or maybe it has)
That's why it hasn't been manufactured.