Under pressure, but is it enough?

T4Syncro · 21 July 2016, 11:14

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

Chris · 21 July 2016, 12:14

Surely its the static reading you take.

Fenlander · 21 July 2016, 12:27

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.

T4Syncro · 21 July 2016, 12:37

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.

Fenlander · 21 July 2016, 12:46

>>>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?

T4Syncro · 21 July 2016, 13:03

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.

The Gurnard · 21 July 2016, 13:55

Quote:

Originally Posted by T4Syncro

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.

T4Syncro · 21 July 2016, 14:06

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...

Fenlander · 21 July 2016, 14:23

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.

T4Syncro · 21 July 2016, 14:34

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.

jeffstevens763@g · 21 July 2016, 19:19

I be been driving sibs for years the guys are right but if carrying a lot of weight you have to play with trim, usually I have mine on second hole up for a flat level ride but you have to play with it,
soft tubes drag a bit but not crucial but very low keel pressure will induce a concave hull and air collects causing a bubble of air to escape and can cause cavitation and loss off forward motion momentarally
20 hp will struggle and be at the edge with 5 people I would think, 7 your asking to win the lottery without a ticket

Nice to see you back gurnard.

Cheers

T4Syncro · 22 July 2016, 09:21

Jeff, thanks yet again for contributing. I think this thread has deviated a wee bit from what I hoped was my main point which is the nose digging in and impeded progress. When I moved the pin one hole out the prop did cavitate when giving it beans. That didn't happen prior to moving the pin.

From what you describe Jeff I think I'm back to where we kicked off, and I have been reading the gauge wrong, which would give me a keel about 60% of max pressure.

Regarding planing, I am quite frankly staggered it planed effortlessly with 5 up and if I had the trim right we'd have planed 7 up without too much drama. Admittedly at full throttle but I'm not expecting miracles and when I bought it I didn't expect it to plan so easily. the previous owner told me his 14 stone son had wakeboarded behind it and I didn't really believe that. I'm thinking its possible now.

I'm putting my money on keel pressure. I'll get out in it again this weekend and have a play.

Thanks everyone

jeffstevens763@g · 22 July 2016, 10:07

Quote:

Originally Posted by T4Syncro

Jeff, thanks yet again for contributing. I think this thread has deviated a wee bit from what I hoped was my main point which is the nose digging in and impeded progress. When I moved the pin one hole out the prop did cavitate when giving it beans. That didn't happen prior to moving the pin.

From what you describe Jeff I think I'm back to where we kicked off, and I have been reading the gauge wrong, which would give me a keel about 60% of max pressure.

Regarding planing, I am quite frankly staggered it planed effortlessly with 5 up and if I had the trim right we'd have planed 7 up without too much drama. Admittedly at full throttle but I'm not expecting miracles and when I bought it I didn't expect it to plan so easily. the previous owner told me his 14 stone son had wakeboarded behind it and I didn't really believe that. I'm thinking its possible now.

I'm putting my money on keel pressure. I'll get out in it again this weekend and have a play.

Thanks everyone

hi mate i think you have it with the keel pressure as the rigidity of the boat will not be there so causing it to banana as the engine pushes down on the top of the transom if that makes sense hence digging in, but if as you say you do plane with seven up then thats a good set up and a quick fix with the correct pressure lets us know how you get on.

cheers

T4Syncro · 22 July 2016, 10:09

Ches Jeff, I'll report back for sure. Thanks mate

chriswood · 22 July 2016, 20:46

Hi. I had exactly the same problem until I realised that the keel pressure dropped when I put the boat in the water. Also had to invest in a better pump to get the right pressure in the keel. Now top up after 5 mins and its made all the difference!! Hope that helps

The Gurnard · 23 July 2016, 17:51

Quote:

Originally Posted by T4Syncro

From what you describe Jeff I think I'm back to where we kicked off, and I have been reading the gauge wrong, which would give me a keel about 60% of max pressure.

Yup.. after reading what you are saying..if you have 60% air in the tubes as well as the keel because you were reading the gauge wrong....Im surprised it planed at all.

As mentioned mine isnt so pressure sensitive ..I just give it the "thump test" to check its pressure.. and its the exact same boat as yours .. but that difference in tube and keel pressure would matter...it would feel soft

im sure you will find it goes a lot better with better pressure

T4Syncro · 24 July 2016, 10:19

Thanks again all. I'd completely forgot that the sea temp will have that effect. By the way, what pump did you buy?

jeffstevens763@g · 24 July 2016, 18:42

I use a bravo but my boat stays inflated some have had issues with them especially those pumping up each time they go out but I guess there's good and bad in all makes. The one I have you set the pressure and wait till blown up and it cuts out.
Might be telling you to suck eggs remember to inflate equally all compartments because if not the baffles get strained and risk bypassing. And the chamber with least air in is more pressure sencertive to cold.

Cheers

roody262 · 24 July 2016, 21:08

I bought a pressure gauge for mine, it's a sevylor one (they make inflatable kayaks etc) comes with a few different nozzles for different valves and is cheap compared to some.

chriswood · 25 July 2016, 00:32

Hi. I bought a quicksilver stirrup type pump with a in-line pressure gauge. Purchased via eBay from Pacer Marine. Cost £30. Comes with all different attachments for all types of valve. The manufacturers foot pump provided with the boat didn't provide enough pressure for the keel but the quicksilver is perfect to keep in the boat and top up while on the water.