Planing Dinghy: Hp vs Dinghy type vs #Passengers

[Jammer]

Originally Posted by Dallasron

While there are those who want the minimum, I have always wanted as much as I can handle in size, hp, and weight.

A primary goal for us is to maximize seaworthiness and minimize windage on the mother ship. Another primary goal for us is to avoid choices that lead us towards a larger boat than the 38' we have now.


In these regards the best dinghy for us would be a 3.1 meter inflatable floor and we may well experiment with that at some point. The problems with them are that they do not hold up well with repeated beaching, especially on the jagged rocky shores that characterize much of our cruising grounds, and they are motor dependent.


A secondary goal for us is for the dinghy to be able to be portaged to allow upriver explorations that would be otherwise impossible.

[wingssail]

Originally Posted by Jammer

A primary goal for us is to maximize seaworthiness and minimize windage on the mother ship. Another primary goal for us is to avoid choices that lead us towards a larger boat than the 38' we have now.


In these regards the best dinghy for us would be a 3.1 meter inflatable floor and we may well experiment with that at some point. The problems with them are that they do not hold up well with repeated beaching, especially on the jagged rocky shores that characterize much of our cruising grounds, and they are motor dependent.


A secondary goal for us is for the dinghy to be able to be portaged to allow upriver explorations that would be otherwise impossible.

Jammer, we have had inflatable floor dinghies for over 27 years (two of them, an Avon and a Zodiac). We have beached then on all kinds of shorelines, from harmless sand to jagged rock and coral. We've used them continuously on a circumnavigation and now use the Zodiac in Mexico.

The bottom of the dinghy IS NOT the problem. The bottoms of both dinghies held up perfectly. On our Zodiac, which is not a particularly good dingy, the bottom is perfect after 13 years. It is the topsides and the inflatable floor which suffer from wear and damage.

There are two reasons why the bottoms hold up so well:

• The dingy is light and we lift it over rocks and coral
• We have large wheels on the transom and we roll it over everything.

There are other reasons for some people to avoid inflatable floor dinghies, but worrying about the bottom should not be one of them.

Photo (2022): Sorry I don't have a picture of the bottom but it looks like new. But as you can see the topside is a wreck after 13 years but it still serves us well (and it FLYS with 15 hp 2 stroke).

[sailhand]

Design and hullshape have a huge impact on performance. Just add more grunt to go faster is true in almost every case, be it a car a plane or a boat. You need to compare apples to apples to get an accurate picture. Most cruisers tend to go the rib and 15hp style of tender. It has advantages and disadvantages depending on your perspective. Lets take for example a 10ft rib with a 3.5hp. Put two people in there and some gear and your hitting warp speed at somewhere around 4 knots. My hard dinghy is longer at 11 foot 6, wider at 5 foot 8 and planes two people with some gear with the same 3.5 at around 9 knots. Seems to me that design has a huge impact, in some cases moreso than power. The same 10 ft rib with two people and a 6hp, almost double the power, will still not plane in most cases. Design is absolutely critical, however enough power will push anything. An efficient lightweight hull and smaller motor, that still has room and reserve load carrying capacity suits my needs as a cruiser. Easier to lift and stow, easier to move on land/beach, less fuel used stored and purchased, infinitely better to row etc etc etc. Im not really sure where the inflatable rib is better other than bumping into things with its big rubber fender and in some cases stowage. I suppose if you want a heavy hull and a big motor to push it they are fine particularly if you are worried it will damage your boat. My dinghy goes marginally faster with a 40 lb min kota than the same size rib with a 6hp and two people. I know because we raced to see which was quicker. The best way to get an accurate picture is to use the same size motor on different boats and then compare performance. I can row faster than a small inflatable with a 2.5hp, much faster and over a two mile distance. I could rest and wait for the inflatable to catch up and then row away from them again. On smaller vessels an inflatable is often the only tender that can be stowed aboard on passage and I carry a 9ft inflatable and spare motor in a locker as an emergency back up. Inflatables are definitely the best option in many circumstances but efficient hullshapes they are not. Just try to row one. Hull design makes a massive difference

[contrail]

Our P.O.S Zodiac 12' Air-Floor dingy planes well when everything is pumped up hard.up the beach, even old folks can with big wheels on it. You'll appreciate that when you try to pull your 2.8mt RIB with a 4 stoke motor and a tank of gas and some "stuff".Having to inflate it

• Miss-named inflateable, should be "deflateable" They leak!

[/QUOTE]


20 years ago, I had an Avon air-floor, with the air-floor made by Zodiac and thus PVC. I loved how that dinghy performed, but yes, the floor and keel leaked and were a constant pain.



I now have an Achilles air-floor, completely made of Hypalon, and I have inflated the floor once a year! Planes nicely. Might be worth a try.

[Jon Hacking]

Originally Posted by Jammer

Realizing that mine is a minority opinion, I believe that a displacement-speed dinghy is a reasonable alternative, especially in the USA. Most of the USA cruising grounds (aside from southern Florida) don't require long dingy rides. CF has a structural bias towards Caribbean and South Pacific cruising. In, say, the Chesapeake, or the Great Lakes, the underwater topography is steeper, anchorages are deep, and long dinghy rides aren't necessary.

While all of what you say is true, & certainly a valid point of view for many, it's also true that there's a tremendous amount of inertia involved in picking up the boat, readying it to move, starting the engine, picking up the hook, going around to the next bay, & dropping & setting the anchor.

When we anchor, we tend to stay there for some time. Our dinghy is our exploration vehicle. While smaller ones aren't necessarily less reliable, we tend to think of them that way, as we have to run them harder.

Therefore, for a true blue-water cruiser, I'd recommend something you'd feel comfortable going ~5nm one-way in now & then, or even longer if you can, assuming you can carry it safely. For a normal cruising couple, this is probably ~15hp, on a tinny if you're Down Under, or (ideally) an alloy-bottom RIB for the rest of us (& yes, I realize that costs & other factors will affect this in many ways - this is just my opinion).

When we left in 2001, we had our 2 adult-sized teens on board, so we needed a 3.4m RIB & 25hp to plane all of us & all our dive gear into a stiff chop. Yes, it chewed through fuel, but it was a lovely beast & I was very proud I'd bitten the bullet at the beginning (which I often don't do).

But my point is that our dinghies don't just take us to shore & back. They're also our exploration vessels, our dive platforms. I'd recommend that blue-water cruisers not skimp on their dinghy. You'll be glad you didn't.

[Tupaia]

Originally Posted by Jon Hacking

But my point is that our dinghies don't just take us to shore & back. They're also our exploration vessels, our dive platforms. I'd recommend that blue-water cruisers not skimp on their dinghy. You'll be glad you didn't.

Your point is absolutely valid. We set off with a small dinghy and a 4hp Johnson outboard (yes it was a long time ago). The setup was more than adequate for N.European cruising with just the two of us.



One visitor and a windy anchorage and it was a total flop. Upgraded to a rib and 10hp. Adequate for two including dive support and we have a second for visitors.


It depends on you circumstances and where you sail.


But once you venture further afield the dinghy is not just for getting ashore it as you say, your expedition vessel, your supply boat, your tug and your kedge deployment vessel. A rubber ring with a puny outboard just does not cut it.

[BenBowSirocco]

GoDu 10.5

(all aluminum "RIB type": 172lbs)

15hp Tohatsu



Planes with 4 people no problems- even in big chop and stiff breeze.



This is our own design and just coming available for sale, but we spent huge amounts of time and effort to improve upon the already awesome modern RIB.

https://goduadventure.com/

[Adelie]

I can't find anything on GoDu.

From your description it is a rigid dinghy formed in the shape of a RIB.
Is that correct?

[BenBowSirocco]

Correct: Its an aluminum non-symmetrical octagonal tube on a high deadrise aluminum hull.


Has easy planning abilities from the tube acting as lift strakes.

[Adelie]

Thx for clarification.

[Tupaia]

Originally Posted by BenBowSirocco

GoDu 10.5

(all aluminum "RIB type": 172lbs)

15hp Tohatsu

Is that the all up weight including the motor (Tohatsu 15hp 2S = 90lbs)?

[Franziska]

Custom Spindrift 10 with Laser dinghy deck and Suzuki 4Hp 2Stroke (with wings) and sparefuel tank in the bow.
Built from plywood, glassed over inside and outside.

Have no way to weigh it, but anticipate it to be a bit heavier than the original design due to the fully enclosed deck.
Original weights about 50kg, so ours is perhaps 60kg. Motor weights 21kg, fuel tank & anchor & chain perhaps another 10kg. Passenger 70kg. So a total of about 160kg.

Gets on a plane and does about 8kn with one person on-board.
I feel 6Hp would get it to plane with 2 people on-board.

Btw. I learned that dinghies not living up to speed expectations are often suffering from a spun prop (rubber propeller bushing is broken).

[BenBowSirocco]

Originally Posted by Tupaia

Is that the all up weight including the motor (Tohatsu 15hp 2S = 90lbs)?

No. That is the empty boat weight.



The boat with bumper and SeaDek is 172lbs.

[Tupaia]

Originally Posted by BenBowSirocco

No. That is the empty boat weight.



The boat with bumper and SeaDek is 172lbs.

That is about the same weight as a fibre glass bottomed inflatable so I don't see the advantage. My own ali / inflatable is 34kg (75lbs) less than half the weight. (26kg outboard, 5kg for the fuel tank, anchor and chain 5kg = 70kg (155lbs) all up)

Maybe it has other advantages but can't see this being useable by a couple doing a beach landing in surf.

So what makes it different?

[Adelie]

Originally Posted by Tupaia

That is about the same weight as a fibre glass bottomed inflatable so I don't see the advantage. My own ali / inflatable is 34kg (75lbs) less than half the weight. (26kg outboard, 5kg for the fuel tank, anchor and chain 5kg = 70kg (155lbs) all up)

Maybe it has other advantages but can't see this being useable by a couple doing a beach landing in surf.

So what makes it different?

All rigid, so no inflatable tubes to puncture on rocks or seams to fail due to age.

Stronger/tougher, longer lasting product at the cost of more weight and more storage volume required.