Newbie Question...

maz · 29 July 2012, 13:02

Having repaired the mouse hole and fully serviced the engine I took my SIB out on the estuary last night to test all is well. I'm pretty happy with everything but when I gave it the full beans on the throttle the boat planes quickly but the floor feels like it's got a big bubble under it nearly all the way to the back. It starts by undulating and then stays kind of bulgy. Now the boat felt stable but as I've gone from rigid boat to SIB I'm not sure if this is normal.
The boat is a Plastimo Raid P270SH and has 3 boards in the floor with gaps between them. The water and wind were very calm and I am 13 stone and was sitting on the thwart. The engine is a Mariner 5.
My satnav clocked me at 20mph which I'm more than happy with.
Is this just what they do? Thanks for any advice....

lockieboi · 29 July 2012, 13:11

If its a inflatable floor then that's normal, they all do it.

Just make sure you get the floor up to the right pressure and that should help.

lightning · 29 July 2012, 13:15

That's quite a speed with a 5hp, I couldn't get over 15mph on my 2.8m SIB with a 6hp on it.
I assume the Plastimo has a flat keel with inflatable floor, which is not ideal for planing. My Zodiac has an inflatable keel under the floor. It's possible you may be exceeding the design speed of your boat, which is primarily designed as a tender.

Does it have an inflatable keel or is the floor flat underneath?

maz · 29 July 2012, 13:16

No it's not an inflatable floor. It is just flat PVC with 3 boards.

lightning · 29 July 2012, 13:17

Probably as above then.

When I was buying my SIB I was told you needed a shaped V keel if you wanted the boat to plane properly and be stable.

20mph is some going though. Have you tried backing it off to say 15mph. What's it like then, any better?

maz · 29 July 2012, 13:26

I should have said that; it only seems to happen at full speed.

lightning · 29 July 2012, 13:29

Possibly exceeding the designed maximum speed of the boat.

What do others think?

maz · 29 July 2012, 13:41

Good point but it's rated to take a 10HP. I dread to think how fast that would go. I was surprised at how fast it went with a 5. Maybe I'm just being a bit of a wuss!

lightning · 29 July 2012, 14:29

That's amazing performance though. My Zodiac managed 14mph flat out with a Mercury 6hp on.
That was with 2 of us on board, combined weight 21stone.

With just me on board it did not really go any faster, about 15mph on the GPS.

The boat is rated to 8hp maximum and I have a 9.8 on it now, but I bet it still won't do 20mph.

However with the inflatable keel and solid floor it handles really well at max speed. So it should though, it cost me £1,000 just for the boat.

maz · 29 July 2012, 14:53

This is the floor. Hope the photo attaches! Lightning, to be fair there was almost no wind and the water was like a mirror.

willk · 29 July 2012, 15:04

My 2.7m airdeck with a 9.8hp made 20.7mph in perfect conditions. I'm a similar weight to the OP. I'd have a bigger chance of walking on water than getting that performance with a 5hp.

Maz - you keep on doing whatever you're doing

Max... · 29 July 2012, 15:29

More surprise here! My 3.4 with the Tohatsu 9.8 and 1.5 people tops out at 17.5 kts (20mph). Air floors are prone to the water bed type ride but max pressure and careful weight distribution will cure it (for the most part).

maz · 29 July 2012, 15:59

I should point out that I hit 20 mph but full speed was mostly 18-19mph. I'm man enough to admit I wouldn't fancy going much faster in that little boat.