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Old 13 June 2016, 10:32   #1
Country: USA
Town: Southern California
Length: 3m +
Join Date: May 2016
Posts: 34
First time out, ran into some plane and comfort issues

Hey guys.

I took my boat out for the first time and decided to take it out into the ocean. I will say the inflatable was a beast to setup and disassemble every time but I realized I forgot my Bravo pump the moment I unpacked the boat. I had a blast though.

A few issues that I ran into. I'm running a 14 foot boat with a 15 HP 2 stroke. This was extremely difficult to plane. I could get it, but after catching a good wave or literally scooting as forward as I possibly could to where my hand was barely on the tiller. Seemed dangerous. I also had 6 gallons of fuel and some other gear (maybe 25 lbs) near the bow.

Somewhat frustrating as when I had it at maybe 80% throttle doing 16-17 mph, the boat was somewhat manageable but a little squirrely. However, if I caught some bad waves, the boat would lose plane and it would take me another 15-60 seconds to gain plane again. I'd only get maybe 30-60 seconds of planning and would run into this issue.

At WOT, this thing was downright scary. I was hitting about 20-21, but it's all OVER the place. Hard to even maintain a straight line. And at times I just thought the floor or transom was going to snap in half. I would ultimately slow down as I was destined to be bucked off at some point. Not if, but when.

I have not messed with the tilt on the motor, as I was starting to get tired so I headed in. I'll adjust that next time to see if that helps. The waves weren't bad, maybe 2.5 foot swells. Somewhere around there. So...

  1. Does anyone have suggestions for me? I've done some research but wanted to know if anyone had some other tips or tricks.
  2. Also, how do you guys stay comfortable? I was on there 2 hours and was exhausted. It's extremely awkward sitting on the tube with few ways to brace yourself. I even tried sitting in the floor and just was getting tossed around.
  3. Suggestions on how to get to plane quicker? As mentioned, I'll try the tilt on my motor to see if that helps. My boat would just squat at WOT.
  4. Lastly, is it unusual for you to have to have the tiller at an extreme angle while trying to gain plane? I'm guessing because of my weight on one side of the boat?
  5. Thanks! Ridiculously long post, so thanks for reading.

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Old 13 June 2016, 10:44   #2
Country: UK - Wales
Town: Cardiff
Make: Avon
Length: 3m +
Engine: 2 stroke
Join Date: Aug 2014
Posts: 489
Hmm sounds odd photos will help. I'm no sib expert but 14' (4.2m) is a fair size for 15hp 25-40 depending on loadings ???

I think the unstable bit is called chine walking, someone will confirm.

A few things to consider:

Is the motor the right shaft length? If it's a long shaft you may have issues

What prop? Pitch and blades?

Try taking a buddy sat up front on opposite tube to level you out. A tiller extension that allows you to sit more central may be needed. Or ballast up front a good anchor with a decent length of chain might help add the lbs where needed.

Was the boat flexing when you went over a wave? Solid floor? Inflatable keel?

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Old 13 June 2016, 11:08   #3
Stigomery's Avatar
Country: UK - England
Town: Cambridge
Boat name: SIBylle
Make: Honda Honwave
Length: 3m +
Engine: Honda BF20
MMSI: 235915576
Join Date: Oct 2015
Posts: 366
What boat is it?
Was everything at the correct pressure?
Tilt (trim) of the engine...

Those are 3 first places I'd look... Regardless something doesn't sound right.

Pics of your set up?
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Old 13 June 2016, 11:41   #4
Country: USA
Town: S. Carolina
Boat name: D560
Make: Avon
Length: 5m +
Engine: Merc 100hp
Join Date: Aug 2013
Posts: 768
Operator fatigue is very high on sibs. it takes a lot of muscle to run a tiller in rough seas.

It sounds like your tube pressures were not completely correct. If under inflated, it can make the boat a rougher ride than usually. The added drag will also make the boat more difficult to plane.

For operator position, sit on the floor and use your feet to push off the tubes to brace yourself.. Make sure to sit on a thick cushion.
Gluing geek since 2007
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Old 13 June 2016, 11:46   #5
Country: USA
Town: Southern California
Length: 3m +
Join Date: May 2016
Posts: 34
Hey everyone. Thanks for the quick replies.

- It's a Bombard Typhoon 420, Alum floor.
- Correct pressure, not sure. I left my Bravo at the house and simply used the foot pump and didn't stop until it wouldn't go anymore.
- It's a short shaft. Other than that, I have no idea about the prop or angle. It was donated by my father and I'm honestly not an expert with outboards. He used it on a very similar sized inflatable, but he isn't sure if he had problems like that. Probably not as he had us kids on it and very flat water in the lakes. I can check the blade (if those specs are on it?) when I get home.
- I can attach a picture when I get home as well.
- Lastly, it got moving pretty good. I was hoping for 20 and surprised I got 21. Just scared the hell out of me is all.
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Old 13 June 2016, 12:02   #6
Country: UK - England
Town: Retford
Boat name: Spy-sea-one
Make: Mercury
Length: 3m +
Engine: Suzuki Outboard/25/4
MMSI: 235074042
Join Date: Oct 2011
Posts: 2,148
The typhoon has a max of 25 hp I think a 15 should be ok and the speed your getting is good it doesn't sound as if the keel is pumped up properly which will give a bad track and the floor moving about. Getting back on the plane might be due to the trim try the second hole up first then the third which will push the bow down. If the sea is rough you will have problems holding on but keel and tube pressure critical.
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Old 13 June 2016, 12:27   #7
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,851
I think 15hp is not enough. Sibs are not efficient hulls and have a lot of drag nor are they very directional because they are flexible and the keel line is very rounded, also, the hull will turn into a gull wing section because it's simply a piece of fabric being pushed upwards by the water. Because the hull pushes up it gives two other characteristics; Number one, as well as the gull wing shape it forms a bit of a tunnel hull between the hull fabric joint and the tubes and secondly, in a side on view the hull fabric is flexed upward but has to curve down to the transom and this forms a hooked hull shape at the stern. Plus, of course, any wave under the boat will effect the hull shape at that moment in time so, in effect, the hull is constantly changing shape under the various loads produced by the waves. That's why the equivalent sized small rib is so much better a hull than a sib. This doesn't mean you can't improve your boat but at a distance we can only guess at a solution for you.
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Old 13 June 2016, 12:38   #8
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Country: UK - England
Town: Derby
Make: Zodiac + Aerotec
Length: 3m +
Engine: Suz.20hp+Toh.9.8hp
MMSI: 239711398
Join Date: Sep 2013
Posts: 283
First time out, ran into some plane and comfort issues

Sorry to hear you're having teething issues. All good advice so far and here's my two cents worth.
Pump up to max. pressure - 90% of a sibs performance is in the last 10% of pressure. Re-check pressure and top up if necessary after 15 mins on water.
Mount motor on transom (raise if necessary) so AV plate is either level or just below transom keel.
Trim motor so AV plate is parallel to water on plane ie leg is at 90 deg to water.
If solo get some weight up front- anchor, fuel tank etc.
If choppy sit on the floor - I always do, one foot braced against transom to keep me pushed forward and the other against opposite tube. Hang on to seat/grab handle with free hand, and relax it's fun.
Ally floored sibs will get horrendous cracking sounds when bouncing off waves and chop. If pumped up hard will be fine. Edges of material floor slaps on u/s of deck and ally floor creaks against transom joint - nothing to worry about.
Have fun and hope you get sorted.
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Old 14 June 2016, 00:49   #9
Country: USA
Town: Southern California
Length: 3m +
Join Date: May 2016
Posts: 34
Thanks everyone. I'll try the items suggested. I'll ensure the keel and all tubes are properly inflated. My Bravo would have been in handy.

I've attached a photo of the motor in the water. It looks a little deep. Maybe a lot deep? It actually looks inches below what it should be. Looking at my manual from 1988 as a reference. See attached.

**EDIT** So what the heck. Took a little trip into the garage and I'm stunned. I measured where the water line is, essentially that nut on the far left, down to the anti cavitation plate and it measures a whopping 8 inches! So I'm way deeper than it should be. Right? It suggest to bolt a block of wood, but I ain't getting that kind of height.

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Old 14 June 2016, 01:04   #10
Country: UK - England
Town: East Anglia
Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
Engine: Suzuki DF20 EFI
Join Date: Nov 2007
Posts: 2,487
I wonder if you were in the boat when the image was taken? The important position of the AV plate (with the two visible extra bolts) is when on the plane and they will sit deeper at rest... but that looks very deep if that's just the weight of the outboard on a 4.2m.

Everything else has been covered really... inflatables are a bit like you describe if compared to a hard boat... knowing the actually (not guessed) pressure is crucial before deciding if you have a problem... your outboard is a little small for a 4.2... one up with fingertips on the tiller trying to get weight forward is not great for control.

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