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Old 29 April 2014, 16:22   #11
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Yep, not good, keep it at idle or 1/4 throttle max in the bin.

As I say, stick a tiny tach on it, go out on your own and see if it comes close to the typical 5500 at WOT.
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Old 29 April 2014, 16:33   #12
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Our 3.6m fastroller and 9.9hp 4stroke Mariner carry 3 of us plus bits (estimated 200Kg plus boat/engine) very quickly (within couple of seconds) onto the plane.

Are you sure you still don't have your launch wheels down...
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Old 29 April 2014, 16:36   #13
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Are you sure you still don't have your launch wheels down...

We've all been there, nothing to be ashamed of!
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Old 29 April 2014, 16:51   #14
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Originally Posted by Fenlander View Post
T4Bus have a look at this Youtube of our Zodiac 360 Fastroller (with Acti-V floor).

It is carrying a load of approx 32 stone in one adult, two girls, extensive bag of kit/anchor etc and fuel. You will see the Mariner 15 2-stroke easily pops it on the plane in about 4 seconds from opening the throttle. It didn't make a big difference whichever trim posn you were in.

There is something odd about the poor performance you're seeing with yours.
Thank you for the vid
I'm beginning to think my expectations are too high & lack an understanding of what constitutes planning?
So I hear statements like "off like a robber dog etc" but then see this vid showing an inflatable cruising, not running it down but robbers dog it is not, I'm genuinely ignorant with this and trying to educate myself, but I believe that being "on the plane" is when the boat overtakes it's bow wave, however your vid clearly shows a nice bow wave being pushed from the front 3rd of the dinghy, so to my mind displacing water? Maybe the issue is me & not the boat, I expected to see only a wave from the back & to feel it a little higher in the water, I should perhaps measure it's speed 2 up & see what it achieves, would guess about 20mph would be about what I should expect, but it seemed slower, possibly due to very still water.
Vid does give me a clearer perspective as most on youtube are in choppy water which gives an inflated sense of speed.


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Originally Posted by Landlockedpirate View Post
Prop - 1st number is the diameter, 2nd number is the pitch. I think the standard prop on yours is a 8" X 9". If its significantly different (either up or down) it can easily bugger up the performance.

Next question, are you sure its a 15hp ? The 8hp was the same shape and block.(Really not trying to be insulting, just thinking of all possible problems)
Not insulted at all, you guys are only trying to help & it's appreciated. I did wonder if the motor was a genuine 15hp, the disc on the cylinder barrel and the chassis plate on the bottom half match numbers, it has a later year hood than a 1996 should have, I assumed the original may have been damaged at some point, but the bottom end looks to be original paint in which case it's in lovely condition.

I'll take it into the shop and get somebody to give it a once over & If all is well maybe we should all get on a diet!
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Old 29 April 2014, 16:58   #15
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Yep, not good, keep it at idle or 1/4 throttle max in the bin.

As I say, stick a tiny tach on it, go out on your own and see if it comes close to the typical 5500 at WOT.
Oops! I ragged it a bit in the bin, maybe why it died & would not idle after? Hopefully seems to run OK now though but I'll try it over the weekend. I didn't think I was being brutal but I'm used to Motocross engines & appreciate 4 stroke should not be revved hard when not under load, but with 2 strokes (Bikes) you can happily rev the cans off them to clear them through, no valve bounce to worry about.
If I've not trashed it I'll be more sympathetic with it in the future.

I'll try the tach, good idea thanks.
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Old 29 April 2014, 16:58   #16
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You'll know if you're planing, difference between displacement and planing is night and day. Dont get too hung up on descriptions of take off, lightly loaded SIBs can be nippy but rocket ships they ain't! A 3.4m with 9.8 will (measured with a GPS remembering this is 'FIBnet') top out at 17 to 18 kts. A 15 on the back will only see a couple more but getting on the plane is quicker/easier especially when loaded up.
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Old 29 April 2014, 17:19   #17
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>>>but then see this vid showing an inflatable cruising

Yes well... cruising on the plane if you like.

In that video I open the throttle at 21sec and by 25 sec it has lifted onto the plane having passed quickly through displacement speed. By 27 sec it has totally flattened out on the plane and from there on was running at about 18-20mph (GPS was set to MPH and I have the track data still on the laptop and have just looked).

That was not far off the max speed for that outfit so if you are expecting much more excitement you need a speedboat!

When I refer to being on the plane as shown in that previous video it is what everyone on here and all boating folks would say is being on the plane.

An inflatable is a big squashy crude shape with a near flat bottom so unless very lightly loaded (i.e. one child at tiller) they will have a bit of tube in the water and produce what you are calling the bow wave.

If you consider watching the wake in this video the boat of mine is on the plane from about 6 sec onwards....

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Old 29 April 2014, 17:33   #18
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Install an induction tach, go for a wot spin you alone and lightly loaded sib on a flat calm no windy sea cond and check max achieved rpm, will know if you have a healthy engine delivering near or full wot rpm factory stated for that engine. You could have a spun prop or in its way of being so.

Factory delivered props on light sibs not heavily loaded, should perform quite well with max 3 adults.

Happy Boating
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Old 29 April 2014, 17:46   #19
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Quote:
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>>>but then see this vid showing an inflatable cruising

Yes well... cruising on the plane if you like.

In that video I open the throttle at 21sec and by 25 sec it has lifted onto the plane having passed quickly through displacement speed. By 27 sec it has totally flattened out on the plane and from there on was running at about 18-20mph (GPS was set to MPH and I have the track data still on the laptop and have just looked).

That was not far off the max speed for that outfit so if you are expecting much more excitement you need a speedboat!

When I refer to being on the plane as shown in that previous video it is what everyone on here and all boating folks would say is being on the plane.

An inflatable is a big squashy crude shape with a near flat bottom so unless very lightly loaded (i.e. one child at tiller) they will have a bit of tube in the water and produce what you are calling the bow wave.

If you consider watching the wake in this video the boat of mine is on the plane from about 6 sec onwards....

That appears significantly quicker than I believe mine was moving, I'm not so much looking for a rocket ship, more ensuring that the motor is well before I use it in the coast with the kids in the summer, My motor pitch did increase noticeably when I sat forward to the point that I could just reach the tiller.

The most significant point is that 3-4 up there is no doubt we were just making more noise, putting greater strain on the motor but ploughing water like snow.

Appreciate all the input, think it's purely a case of taking this on board & sticking the motor in to get checked out at the shop, I'm reasonably competent around small engines but I think with a lack of experience with this I should accept defeat & pay the experts to check it over properly, if it's OK & legitimate them maybe we need to lay off the pies.

Thanks for the advice and videos, very helpful. Roll on Summer!
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Old 29 April 2014, 17:47   #20
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Install an induction tach, go for a wot spin you alone and lightly loaded sib on a flat calm no windy sea cond and check max achieved rpm, will know if you have a healthy engine delivering near or full wot rpm factory stated for that engine. You could have a spun prop or in its way of being so.

Factory delivered props on light sibs not heavily loaded, should perform quite well with max 3 adults.

Happy Boating
What's a spun prop?
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