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Old 10-10-2014, 16:09   #1
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Why is Planing Ability Important in a Dinghy?

Planning to live aboard full time in the near future and have started looking at dinghy and motor options. I'm pretty much settled on a 10' RIB from AB, Achilles, or Apex. The boat has an engine crane but no davits or arch and adding them is not a high priority so the dinghy will be deck stored. I need to carry wife, child, self, and payload (groceries, water, fuel).

The widespread consensus among most RIB fans seems to be that you'll want or even need to plane and that anything less than a 15 (or even 20) HP motor will be a disappointment. I'm curious as to why this is?

Not (yet) having been indoctrinated to this way of thinking, a 15 HP on a 120 lb. boat seems like an enormous amount of power and it also seems like an enormous hassle to continually be craning an 115 lb. motor on and off. Being a sailor, I don't have a need for speed and the notion of zipping around in shallow waters on a very light boat at 15-20 knots actually seems a little frightening.

So I'd welcome those who say "go big or go home" to educate me on the benefits of being able to get on plane. Otherwise I'll buy a 6 HP motor and call it a day!
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Old 10-10-2014, 16:17   #2
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Re: Why is Planing Ability Important in a Dinghy?

I have a 10' RIB and a 4 stroke Yamaha 8 and I can plane only when alone or with small load. But... the need to plane and go that fast depends on where you are. Most anchorages frown on speeding such as planning and where I am moored the speed is limited to 5mph. So there is no possibility to legally plane even if you could.

If you are anchored far from a destination planning might make sense if the sea is flat enough. I don't know how much more a 15hp weighs and I use a lifting crane... but the 8 is fine for my needs and I been dinghying for 28 yrs in all sorts of configs. I do like the hard bottom 3 chamber inflatable though.

Of course others cruisers will tell you something else.
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Old 10-10-2014, 16:21   #3
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Re: Why is Planing Ability Important in a Dinghy?

You might find a friend that has the set up you are considering and let him/her take you for a ride. Will 6 hp be enough to move you through the water against the wind and 5 knot current? I like to row to a mooring. It makes a big difference when I add just another person. Against the wind and current, it becomes a chore.
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Old 10-10-2014, 16:29   #4
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Re: Why is Planing Ability Important in a Dinghy?

Too much to store on deck. Could you put that on deck alone? I doubt it. Donyou want tonjer the engine on and off every time? How long until ou wrench your back or drop something?

A. Get davits. You'll be glad. The dingy is the family car.

B. If not, get a rigid floor (not RIB, not roll-up) with a small motor.
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Old 10-10-2014, 16:31   #5
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Re: Why is Planing Ability Important in a Dinghy?

It depends on what you like to do. But I have gone probably 10 miles from anchorage exploring and snorkeling etc. At 15 mph it's a breeze. If you buy a lightweight single floor RIB, 10 hp might get you there... but most 10 hp are same weight as a 15 .. so why not? a 5hp on an air floor dink would plane me alone. I had the 15 Yamaha on a 9 ft RIB for a while and it did borderline on being too squirilly for sure. A 10 ft with a 15 just seems the perfect thing. Yo might go 2 miles into town for provisions... and then see a thundersquall headed your way as you are loading the dink. With a planing fast dink you can get to the boat before it hits. putting along a 4mph you may not.. and you and all your groceries may be very wet. No big deal at home, but drying wet clothes takes more effort when cruising!
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Old 10-10-2014, 16:34   #6
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Re: Why is Planing Ability Important in a Dinghy?

You don't need to plane all the time, but it can remember more than one mooring where we were anchored a mile or two from town. It's doable at 3 knots, but it gets a little old dedicating an hour to the local dock and back when making grocery runs. The other issue is you need a motor powerful enough to push you into a strong headwind. A small motor may be fine when it's calm, but what happens when you need to get back to the boat into a 25kn headwind.
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Old 10-10-2014, 16:48   #7
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Re: Why is Planing Ability Important in a Dinghy?

You are correct in thinking that if you need to remove the motor regularly, then you should be thinking small (light). Even the lightest 15hp 2-strokes are heavy for this purpose.

The real reason to plane in an inflatable is because they just are not made to NOT be planed. They become real wet and ship water when there is the least amount of chop, wakes or side waves. On plane, they simply ignore all that and shoot over the top of it.

So you either need to go VERY slow or get on plane.

The comments about speed helping in long travels, rain showers, etc are true - but those are all relative (why not 60hp at 30kts?). The real reason is the design.

You might be better off considering a portabote and small engine.

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Old 10-10-2014, 18:19   #8
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Re: Why is Planing Ability Important in a Dinghy?

My mooring is 1 mile from where I park the dink. It's a long ride with provisions, the wife and the dog. I can't imagine a 2 mile run to pick up some grub. Finding a close in anchorage is more sensible them dealing with a very heavy motor and needing to plane... which probably is such an exception as it makes no sense for this to drive your decision.

Yea I can plane with the 8 and make the run in half the time. How important are 10 minutes?
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Old 10-10-2014, 18:20   #9
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Re: Why is Planing Ability Important in a Dinghy?

You get wet if you drive at hull speed but never a drop of spray at planing speed.

My current dink is 9' 6" with an 18hp 2 stroke and its the best investment.

I stay dry and any trip is quick and easy. Many, if not most, anchorages are a nm from where you want to go. Thas 15 minutes in a slow dink compared to 4 or 5 minutes in my dink. 15 mins is a long time to be saturated.

So you get to the dock wet. Dinghy Wet Bum I call it. So you go jump the bus to the supermarket still wet. Your undies stick with salt water. After you dry off after an hour and head for coffee your shorts still have the salt stain around your bum. A nice look... But what about the look of salty bum on your wifes dress? How about that itchy salt on the childs undies. Think of the irritation and how they will complain.

And then you gotta come home!

My first dinghy was all I could afford and a 3.3hp OB. Great engine but it was hell on my GF. So I bought a 9.9 and that was great with just me, but grinds to a halt with people.

The 18 has the guts to get a full dinghy to shore and back with you dry as a bone!


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Old 10-10-2014, 18:53   #10
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Re: Why is Planing Ability Important in a Dinghy?

I'm always amused and, like you, curious about this apparent dichotomy. We have people who have purposely chosen a small sailboat -- possibly the slowest way to travel anywhere -- who then "need" to have a fast zippy dingy to get to shore, buzz the anchorages, or get out to the fishing grounds. I admit, I too don't get it .

FTR, I have a 10' portabote and a 4-stroke 3.5hp engine. It planes with one person in it, and I've even had it up with two adults on flat calm days. But this engine moves us plenty fast with a full load, and so far, no wet-undies syndrome. I can easily lift the engine off and on without a crane. Seems to sip gas. Best of all it rows well, is very tough, and stores well on the mothership.
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Old 10-10-2014, 19:01   #11
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Re: Why is Planing Ability Important in a Dinghy?

I had 12ft with a 25hp engine. I can tell you without that motor I would have never gotten off the beach during a storm. Its all personal choice

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Old 10-10-2014, 19:18   #12
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Re: Why is Planing Ability Important in a Dinghy?

I think it would be very useful to know which respondents use davits and which un-mount the engine each time and invert the boat on the foredeck and lash it down.

Davits? Go for the RIB and big motor if you like.

No davits (this is what the OP asked)? I don't get it. Too much work, I'd rather use a kayak (I have 2 and often use them instead, since they are even easier to use than a dingy on davits).

Yup, once in a while motoring into a big wind you get wet. Woopee. And I've never found a wind my 3.5 hp wouldn't manage at 1/2 throttle; heck, a 10 hp would push a 5 ton boat into a good breeze. It would make a difference if the boat were seriously overloaded, I imagine.
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Old 10-10-2014, 19:54   #13
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Re: Why is Planing Ability Important in a Dinghy?

10'6" RIB, 15 hp Lehr propane, and its nest on the port wing deck. Note the orange rollers. It hoists with the main halyard, coupled with the blue "Goldilocks guy" which ensures a parallel pull over the rollers. Pardon the mess, I am repainting the decks and completing the launch/retrieval system.
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Old 10-10-2014, 20:02   #14
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Re: Why is Planing Ability Important in a Dinghy?

No davits but we have a RIB and take off the motor. We cruise/live on a 31 foot mono. Davits would but too much weight over the stern, inmo.

So we got a 9'6"aluminum RIB and 9 hp 2 stroke ob. Motor goes on the stern rail and RIB is either on the deck or towed. We got the aluminum RIB bc it only weighs 108 pounds. We got the 2 stroke bc it weighs 57 pounds.

MarkJ pointed out the advantage of having a dinghy that plains. We can only plane with one person but the RIB is also more stable and we can beach it on a rocky or shell covered shore.


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Old 10-10-2014, 22:05   #15
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Re: Why is Planing Ability Important in a Dinghy?

Quote:
Originally Posted by Mike OReilly View Post
I'm always amused and, like you, curious about this apparent dichotomy. We have people who have purposely chosen a small sailboat -- possibly the slowest way to travel anywhere -- who then "need" to have a fast zippy dingy to get to shore, buzz the anchorages, or get out to the fishing grounds. I admit, I too don't get it .

FTR, I have a 10' portabote and a 4-stroke 3.5hp engine. It planes with one person in it, and I've even had it up with two adults on flat calm days. But this engine moves us plenty fast with a full load, and so far, no wet-undies syndrome. I can easily lift the engine off and on without a crane. Seems to sip gas. Best of all it rows well, is very tough, and stores well on the mothership.
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