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Old 21 July 2016, 05:14   #1
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Country: UK - England
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Under pressure, but is it enough?

Hi all, we've had a few great outings in the boat over the last week and really happy with it apart from the nose digging in at full throttle and impeding progress and not such a comfortable ride..

It's a Quicksilver 430 with 20 hp Mariner 4 stroke and I think this is one for those esteemed Quicksilver owners among us.

My thoughts were either tube and keel pressure or eninge trim. I was feeling ok with the pressure so last time out I moved the trim out a hole and it spent most of its time with the nose up too high, so that has been moved back to where it was.

So it got me thinking about pressure again. I've got the hand pump with inline gauge and it shows pressure all the time. Obviously this goes up when you pump and I was understanding that this is what I read for the inflated pressure, although never convinced as it varies when I pump harder (bracing myself for comments)

So do I take the static or pumping pressure or am I doing it all wrong?

Thanks in advance,

Dan
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Old 21 July 2016, 06:14   #2
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Surely its the static reading you take.
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Old 21 July 2016, 06:27   #3
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Depends on your pump/gauge/hose setup. With some inline gauge setups on the pump stroke you get a burst of "over-reading" and then when you stop pumping it settles to the true reading.

But if your valve adaptor doesn't hold the valve open then you'll just be seeing the hose pressure which will usually then decay slowly back through the pump.
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Old 21 July 2016, 06:37   #4
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Thanks for replies.

Fenlander, the hose does hold the valve open and the gauge sits at a constant pressure when not pumping, which I thought would be the right reading. However, when I read the manual there is this line, "Note that to read the gauge, you must be pumping the handle." Which I took to be whilst pumping, which as you say gives an over reading, especially if you give it beans.

To me it seems to be when static but I am concerned about over inflating.
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Old 21 July 2016, 06:46   #5
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>>>hose does hold the valve open and the gauge sits at a constant pressure when not pumping, which I thought would be the right reading.

Well that must be the reading of the tubes then. Perhaps the manual refers to a different pump/gauge/hose setup than the one you have. My first Zodiacs had a gauge that only read when pumping as the adaptor didn't hold the valves open... so I can see why a manual might say that.

Re nose digging in... Is this on flat water or does it tend to stuff into waves rather than go over? I forget your crew numbers. What are they, where do they sit and do you think overall you have too much weight forward?

Do you have a hydrafoil on the outboard?
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Old 21 July 2016, 07:03   #6
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cheers for the reply, makes sense to me and would indicate that I am under inflating. Crew has varied from 4 to 7 and we've shifted them and kit around but it still didn't feel quite right as if it was stalling. Sea states have been varied but nothing resembling a millpond.

I'm tending to think I'm not inflating it enough and as I have read on here in numerous places that under inflation tended to be the main cause of what I think I am experiencing.

And no, I don't have a hydrofoil fitted. I'd even forgotten about those, I might go have a read somewhere.
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Old 21 July 2016, 07:55   #7
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Quote:
Originally Posted by T4Syncro View Post
Crew has varied from 4 to 7 and we've shifted them and kit around but it still didn't feel quite right as if it was stalling.
Hi T4Syncro..I doubt it is a pressure problem.. at least my one seems to be happy to perform at various pressures..including recently having a punctured tube which have no pressure in it .. and still performing well.

I think possibly the answer is in your statement above. Too much weight for a 20 hp to plane properly. The SIB is a heavy brute to begin with ..so will be over 150kg for boat and engine ..add 7 folks and its asking the OB too much to perform well.

My 25HP planes no problem with four adults ( and that includes myself as driver.) It get sluggish with many more .. but I have never had more than five in my boat.. as the performance would be crap with my 25HP

but take my opinion with a pinch of salt as I have never tried 7 or 8 in my boat.
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Old 21 July 2016, 08:06   #8
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Thanks Gurnard appreciate the input. The boat planes easily enough with 5 up and we could get it to plane with 7 though we had to shuffle forward a bit. I must admit I wouldn't believe it myself if I hadn't been there in the boat at the time. I must say that none of us could be considered to be carrying excess luggage...
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Old 21 July 2016, 08:23   #9
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Good to see you are about Gurnard!

I'd agree... the last few percent of pressure is usually only crucial in a HP air floor and unless you're running soggy with creases in the tubes I don't think it is the problem. As Gurnard says your load is significant added to the heavy SIB.

However it should be possible to experiment moving folks about to stop the bow going in... or would that end up with everyone huddled around the tiller?

We rarely are anything other than 3 + dog + kit. I'm on starbord tube at tiller... Mrs Fenlander is always on the seat (just one seat posn in the Aerotec a bit forward of centre), the heavy with fuel 25l tank is below her in the fixings provided... medium size dog by her feet... some kit in bow and some under seat. And that just leaves daughter around 8stone who is our moveable ballast either on the opp side tube to me forward of the seat of opp tube just behind the seat if we want to lift the bow a bit in heavy weather.

If daughter is not with us boat is trimmed pretty well spot on with us in out "set" positions.
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Old 21 July 2016, 08:34   #10
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ok thanks again. I'll try further adjustments, my main concern to start with was whether I am getting enough air and if I was reading the gauge right whilst pumping.

I don't have creases or sagging and it looks inflated for sure. I'm still interested in whether I have enough air but cautious of over inflating it.

Regarding performance perhaps I am being over particular about it, having not owned a sib before and all my experience is with solid boats.
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