Dinghy won't plane
mark...@markevans.org
Colin from Moonlight Lady
I very much doubt that you will improve on the manufacturers prop
Mark... I suppose you already thought of ensuring that the boat is
always as flat as possible by balancing the load?
Don't know about RIBs but I suppose it's inflated really hard?
I once had a 25hp in a 14 ft boat. Totally dangerous!
Have fun!
Colin
mark...@markevans.org
From: "Colin from Moonlight Lady" <ad...@bestofshow.com>
Sent: Thursday, February 04, 2010 4:12 PM
To: "Compass Yacht Group" <compass-y...@googlegroups.com>
Subject: Re: Dinghy won't plane
You received this message because you are subscribed to the Google
Groups "Compass Yacht Group" group.
To post to this group, send email to
compass-y...@googlegroups.com
To unsubscribe from this group, send email to
compass-yacht-g...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/compass-yacht-group?hl=en-GB?hl=en-GB
spikec28
I have a light weight tinny about 10 or 11ft long. I bought it off a
mate. It has a 9.9hp motor which apparently are more like 11hp,
they're just called 9.9 for rego (tax) reasons. It planes easily with
one onboard and does 17kn (gps speed). But this mate said it struggled
to plane with two. I have no idea how it compares in weight with a
2.5m RIB.
An old salt I knew years ago reckoned that a lot of small outboards
have fairly crude power limiting devices in them like restrictor
plates somewhere in the induction path or throttle openning limiters
(maybe just a screw). He said he was getting more like 15hp from a
12hp unit with some minor mods. Might be worth a look under the
cover.
Cheers,
Dave.
Kyeemah
I have a 6hp 4 stroke on a 2.4 inflatable (with inflatable keel and
floor). Planes with my son and I (about 115kg passengers). won't do
much better than that. I added a Permatrim plate to the outboard leg
which made a slight planing improvement. Nothing remarkable though.
I am surprised a hard bottom boat with a new 8hp won't get 2 POB on a
plane, though RIBs and inflatables are comparatively short in the hull
compared to a tinnie etc.
There is also the option of simple cavitation plates for the hull.
However, I agree with you. I would expect it to plane with 2.
I supposed you have tried adjusting the outboard leg angle etc? I also
shift weight considerably forward until it is on the plane. makes a
big difference.
I just replaced the prop on my 6HP outboard for $155.00.
Ian
feebz
Hi Mark
just read your post
i have a bit to say on this, but have to run right now i will, will
try and get something up for you by tomorrow,
but just quickly dont rush out and buy the finns just yet
cheers
shane
feebz
Hi Mark
i have already wrote this thread out once, but just
deleted the whole lot, cause it was going on and on, and getting off
track sort of
Firstly, if you have a brand new motor still under warranty,
soon as you drill the holes and or attach the finns to the cavitation
plate you can kiss your warranty good bye, all the people that i know
that have put finns on there boats, say they reckon it kept them on
the plane for a bit longer when they were backing off the throttle,
they had no trouble getting onto the plane befor, it's just that there
boat's bum did'nt pop out of the water quite quick enough for them,
mabee if they move a bit of weight from the ass end and dumped the
water in the live bait tank befor they took off, the boat might of
poped out of the water and onto the plane a bit quicker, e.g 50lts
fuel tank, 15kg battery, esky's, it all adds up, A boat is not like a
car, you just can't throw every thing in the boot, and chuck the kids
in whatever seat and strap them in and take off, as Colin said it's
all got to be placed in the vessel so it stays in trim,and once thats
done, as Ian said you might have to move your body weight around a bit
as the nose comes up as you open up the throttle, and the boat must be
level, so no sitting on the same side, unless you are counter waiting
the beer, also play with the trim bar move it back away from the
transom a hole or two, if it is to low the nose wont lift, making it
even harder for the boat to get onto the plane, if you go to high with
it you will do a wheely and or cavitate the prop
I think you will find that it's not the motor that's holding
you back from getting on the plane, it's more than likely, just the
fact that the IRB (i think thats inflatable rubber boat) was built
with stability & storage in mind, and not high speed planing, and if
the bottoms soft and moves around and wobbles a bit under your feet
that will hold you back as well, and also if your at the back and
your passanger is right up the front, it may be distorting the bottom
of the hull as well, there is a hole lot that comes into it, e.g
wind , tide current, chop, just like the fuel, batteries and esky in
the big fishing boats, it all adds up.
so don't go being to hard on your new boat and motor, just play
around with it for a bit with just you in it, get her humming, then
throw a stunt passanger in and keep moving them around till you find
the sweet spot, and most of all as Colin said have fun
i hope that was of some help to you, there is so many resons why a
boat wont get on the plane, when you think it should be, and without
seeing or hearing it, it's near impossible to tell, it could even be
the length of your leg, it just go's on, but i would say more then
likely it just the design of the hull, and materials used to construct
it,
cheers
shane
Maeling
considerations
Rubber ducks are already heavier than tinnies and probably with less
planing surface. Then the inflatable bottom doesn't hold its shape
like a tinnies. 9hp used to be reckoned as real power to plane, though
a 6hp could just do it with 2 lighter people. Changing slightly
Evinrude put out a 25hp one year. It was the same engine as their 18hp
but allowed to breath harder and get another 1000 rpm and 7hp. A lot
of smaller engines are similarly uprated, there is no substitute for
cubic capacity.
Geoff Raebel
On Feb 4, 10:21 am, "m...@markevans.org" <markev...@markevans.org>
wrote:
mark...@markevans.org
From: "Maeling" <scou...@gmail.com>
Sent: Monday, February 08, 2010 8:21 AM
Lots of good stuff here. Not commenting directly but just some
considerations
Rubber ducks are already heavier than tinnies and probably with less
planing surface. Then the inflatable bottom doesn't hold its shape
like a tinnies. 9hp used to be reckoned as real power to plane, though
a 6hp could just do it with 2 lighter people. Changing slightly
Evinrude put out a 25hp one year. It was the same engine as their 18hp
but allowed to breath harder and get another 1000 rpm and 7hp. A lot
of smaller engines are similarly uprated, there is no substitute for
cubic capacity.
Geoff Raebel
On Feb 4, 10:21 am, "m...@markevans.org"
> Hi
> I've just bought my first outboard and I don't know much about powerboats.
> I've got a 2.5 metre RIB with a 8hp Mercury outboard. It goes like a rocket
> with one person but won't plane with 2. Should I change the prop or is
> there any other way to get it up on the plane? Bloody annoying after
> spending all that money! I would have thought that was enough power and I
> can't afford a bigger one anyway. It would be scary with more power when
> there is just one aboard.
> CheersMark
> PS - I know this is a sailing group but there's lots of boating experience
> out there...
Djarraluda
Your latest post is the give away here. When you state this is the
largest engine recommended, that indicates she is not the "sports"
style, but the tender type of boat.
The difference really comes in the keel. The sports type have more of
a V shape (as well as the greater bracing, rigid transom etc) that
gives more angle in the floor. As the boat speed increases, the bow
lifts and the water movement is both back along the boat and sideways,
which lifts the boat and aids planing. The tender style is not really
intended to plane, but the keel is there to give directional
stability. You may be at top performance for the boat already.
My old 2.5m boat was for diving and I had a 25HP, we planned with 3
divers, but not 4. Had a 16ft in the club with a 35HP and that would
not plane with 4 divers and a Coxn.
It is really about water displacement / power so the underwater shape
is important. 1 trick to try is to work her onto the plane. bum
down, bow up and then lob your crew forward. This literally lifts the
stern out of the water, using the bow wave as the pivot (cause it is
half way down the boat when in the initial attitude.) I always keep
the boat kit and spare fuel forwards anyway, just moving the crew.
One possible trim issue is the angle of thrust. There will be a pin/
peg type of angle adjustment. Not the tilt, or shallow water lock,
but a range of trim settings that may need the engine removed to
adjust. This should be horizontal when the boat is on the plane, but
some adjustment may be necessary to get the proper power to get on the
plane. Worth a play anyway.
Roger
On Feb 8, 10:42 am, "m...@markevans.org" <markev...@markevans.org>
wrote:
> Hi
> Thanks for all the replies and especially Shane's extended effort. I ended
> up fitting the "Permatrim" fin to the outboard. Made a little difference
> but not enough to plane with the wife on board. Not sure what to do now. I
> could get a larger tinnie but that will trash the yacht topside and
> wouldn't fit on the davits. Or I could fit a larger motor to the RIB but
> I'm already at the maximum stated on the little specs plate. I can't
> believe that a RIB rated for 4 adults won't plane with 2 when it's got the
> maximum engine permitted. Groan :(
> I'm not sure if wasting another $200 on trying a smaller prop is worth it.
> Already over $4000 down...
> CheersMark
> PS Sorry I didn't make it to the regatta. To many things to fix to go
> sailing. Maybe next year. Hope you all had a great time.
>
> ----------------------------------------
> From: "Maeling" <scout...@gmail.com>
Mark Evans
head now. I'm especially surprised at the amount of power required. I guess
weight really makes a huge difference especially in a short hull. The RIB I
bought second-hand is a EURO NZ 2.5. It's a beautifully made thing with
quite a noticeable V aluminium hull and an extremely strong transom with
braces. However it's only rated at 8 HP. I couldn't understand that but
maybe you are correct that the V isn't deep enough. I swear the transom
could handle bigger.
But I guess if you go added a 15hp motor then it's no longer a dinghy. You
wouldn't be able to pull it up the beach on the wheels or I could put my
back out struggling with the engine on deck etc. I'm not sure if there's a
way to get around the rego/legal issues either. No easy answer. We could
take one each and have races :) I've got the other inflatable keel
quicksilver 2.4. It really would be nice to have a planning dinghy that
takes the whole family though. Waves just land in your lap when it's not on
the plane.We have to travel a couple of KM from the mooring to the dingy
dock across some very exposed water.
Actually the other day the thing actually managed to crawl on to the plane
with both of us. I'd had it on full throttle for about 5 mins. I was
obviously ecstatic! The Permatrim really makes a difference. Anyway I've
order a prop that is one step slower so I'm hoping that will make improve
things although from your comments about 25 hp and more I may be wasting
more money. I'll let you know...
Cheers
Mark