Thread: Dinghy suggestions?

Originally Posted by Uncle Bob

The must have criteria are:
1) Carry two adults and one anklebiter
2) Be able to fit on a roof rack of a Commodore

The biggest boat which can be carried on roof rack is a Boatmik's GIS (Goat Island Skiff) - she is light enought but bulky... She has a room for 2-3 adults.

The wishlist criteria are:
1) Being able to sail
2) Able to take a outboard, probably an electric for pottering round the Canberra lakes and an 5-10 hp for pottering around down the coast (Narooma lagoons)

She is great sailing boat and is able to use 5-10 hp outboard

The "now he's gotta be dreaming" list:
1) Able to tow a waterskiier
2) Have have the 10 Solid Gold Dancing Girls onboard, giving out teabags

Be realist (your wishes are contradictory ) ... GIS can't take more power and crew ...

Check out it there: http://www.storerboatplans.com/GIS/GISplan.html

Hi and thanks Rob. The GIS looks great, though might be a tad big for the roofracks. Another thing is, this seems to be primarily a sailor and secondary a motorer. I would prefer it round the other way, as my Dinghy may not even be used as a sailor, yet having the option would be great. That said, I'm not discounting the GIS outright.

Howdy Unca Bob,

About 4hp is the maximum that the GIS can handle ...

There is a general problem with most boats that are primarily a motor boat and secondarily a sail boat and vice versa.

Particularly if you want to go at any speed at all in motorboat mode.

You can make a sailing boat go reliably under motor - but your speed is only going to be the hullspeed of the boat or a little more. Any more and the boat will sit with its nose high in the air and refuse to go faster.

Like this GIS - which has quite a small outboard (I don't recommend more than about 4hp and this boat has something smaller) - but the two kids up in the bow are holding the nose down.



This is what happens to any reasonable sailing shape when you add more power - the bow goes higher and you don't go any faster.

The GIS will top out at around 6knots. A shorter boat like the PDRacer will top out at around 4 knots.

Now flipping it round the other way ... a powerboat that is designed to go faster than this will make a crappy sailor.

Here is my Handy Punt.



To allow the boat to go faster without the nose poking up higher the back part of the boat has to be straight. Note the bottom shape furthest away from the camera! Dead straight.

While the boat will perform well at higher speed, when you go slower it will create a lot of turbulence behind the boat.



To create this amount of turbulence behind the boat takes a lot of power - like the motor will be providing maybe 4 or 5 of its potential horsepower to go this fast.

Now consider that a sailing boat in a moderate wind might only have a half horsepower available from its sails - but will move along very nicely because it doesn't create this amount of turbulence.

For example



Note how the stern of this PDR is above the water - it is doing a similar speed to the punt - but because the water can get up to its natural level while following the hull there is much, much less turbulence - thus much less waste of energy.

So if you want a single hulled motorboat that goes fast and sails OK - you haven't got any chance at all - whatever some marketing type with his eye on your wallet might say - or someone who actually doesn't know anything about real sailing performance.

However if you are happy with lower motor speeds to go fishing or whatever - you can use a sailing hull shape - no worries.

In larger sizes you start to have some options as you can move to a multihull design. This can allow quite good sailing performance matched with quite good performance under power.

Two reasons - even though the bottom of the boat comes up to the surface of the water for good sailing
1/ The area at the back of the boat is much less - so less ability to pull the stern down.
2/ The curvature at the back is much less because of the greater length.

Unfortunately this is not available for you if you only want a small boat - because a 12ft multihull will be both a crappy motor boat and a crappy sailor. Get up to 16ft and you can start to do something ... like the venerable Jarcat. Not the best sailing catamaran in terms of performance - but not bad. Not the best motorboat but not bad. With a 25hp a kid can waterski or freeboard - not fast - but enough to have a good deal of fun!



I know this is much more boat than you want to build - but I wanted to show the TYPE that can do both jobs.

Michael

Wow, great post, very informative!
So it's looking like I want to build a small Dinghy that's a crap sailor As long as it works as a fishing platform.
I actually saw something a couple of days ago, can't remember the name, should've bookmarked it. It was called "(ladies name) bay", looked good. I'll go fish through my history and see if I can spot it again.

Edit: Ok found it. It's the Laura Bay. http://www.duckworksbbs.com/plans/me...-9_5/index.htm

Looks a little small, but probably not bad for a beginner. What do you pro's think?

BoatMik, do you have any plans along this shape? I would rather support a local designer before an overseas one, but the design needs to be right.

Originally Posted by Uncle Bob

Edit: Ok found it. It's the Laura Bay. http://www.duckworksbbs.com/plans/me...-9_5/index.htm
Looks a little small, but probably not bad for a beginner. What do you pro's think?

That's a nice looking little boat. Wish I'd seen it before I built my Teal.
Seems to cover the fore-and-aft trim hassles of small boats quite neatly.
9'6" will quickly get squeezy as the ankle-biter grows, and both adults
will need to be careful about their movements to avoid upsets.

Any particular reason it has to go on the roof of the Commodore, &
not, say, on a 6x4 box trailer ?

cheers
AJ

Originally Posted by b.o.a.t.

Any particular reason it has to go on the roof of the Commodore, &
not, say, on a 6x4 box trailer ?

cheers
AJ

The main reason is that I don't have one
I'm thinking if I can keep it small, I'll have a better chance of selling the idea to the missus too, as she's not too receptive of the idea at the moment

G'day uncle Bob,

Check this one out. Not an Aussie, and probably won't sail very well, but still, a very good boat IMHO.

Plans are the right price too.

http://www.jemwatercraft.com/proddet...prod=DKDingy15

bit late but:

if you want something beautiful, cosine wherry. It'll motor and row fine and takes a sail well also. Not the fastest nor cheapest boat to build though. You can get the weight down to 45kg easy for cartopping.

Bob,

I did a Spindrift 11' a while back which might fit the bill. It was made as a tender without sailing rig although the plans do contain the details for the sailing rig. Rows well, motors well and according to the anectdotal evidence sails quite well.

Extremely easy to make. see http://www.bandbyachtdesigns.com/spin.htm

regards,

AD

Uncle Bob,

If you want to keep the weight down explore the possibility of using Paulownia for the framing. I grow, mill and sell Paulownia and quite a number of my sales have been to FM for the purpose of buiilding small dinghys. The designer would be able to determine if it is a suitable timber for your preferred craft.

Contact me if you decide to use Paulownia and I'll help you as much as I can.

hi

the spindrift looks nice and here is a similar boat tough a fraction bigger

as to outboard, would have thought that 3hp would be ideal, is what i have, was only $100 more than the 2hp plus it has neutral as well.

http://www.bateau.com/studyplans/R13_study.htm?prod=R13

There are also long lists of boats as can be seen here
http://www.duckworksbbs.com/plans.htm

there was a page on duckworks that gave a long list of boats that could be sorted via length cannot find now though

other name that come to mind that have many models
selway fisher
william atkins

Originally Posted by Uncle Bob

Edit: Ok found it. It's the Laura Bay. http://www.duckworksbbs.com/plans/me...-9_5/index.htm

Looks a little small, but probably not bad for a beginner. What do you pro's think?

It looks like a sweet little rowing boat for one - but it is having a bit of trouble with two in the pic. So it depends how you want to use it.

MIK

REVISION - just had a look at the web page. The comments I made above about the difference between a motor boat and a rowboat/sailboat shape are particularly relevant here.

The boat has inadequate rocker in the back of the boat for either rowing or sailing. Note how deeply the transom is immersed with only one rower aboard. It might make a good little motorboat with a small outboard - but it won't be a great rower or sailer - particularly with two people aboard.

The transom usually needs to be well above the water with one aboard if you want decent sailing/rowing performance with two aboard.

With the pic of two people - that wide transom looks like it will be a good 9" underwater.

MIK

If you are thinking small and simple - I would suggest the venerable Bolger Nymph.

It comes in at around 40lbs - is the right width to carry by yourself - you put it on its side and put the gunwale on your shoulder.

It won't be fast with an outboard - a couple of horsepower is all you need - it rows well and it can sail pretty well too.

http://euler.sfasu.edu/Nymph/

It usually comes out of 2 sheets of ply - but if you spring for an extra sheet you can make it around 4" wider for more of everything.

It will carry three adults.

The plans are in Payson's "Build the New Instant Boats" - which talk about using polyester resin - if you want the boat to last a lot longer with less maintenance epoxy is the way to go - particularly if you seal the boat as per the manufacturer's directions.

Best wishes
Michael Storer