Sucking feeling while on plane

[nmzodiac]

Just got my new Saturn SB518 out on the lake today. This boat is replacing my old FC470. When I get up on plane around 20 mph I get an undulating feeling in the floor kinda like it is being sucked down. I never had this feeling in the 470 but my new boat doesn’t have speed tubes.
Any of you have that same feeling with boats without speed tubes?

Thank you

[John Kennett]

Is the inflatable keel up to pressure? It’s going to be pretty critical in an inflatable that size.

[Fenlander]

Yes this is something folks have experienced but usually with longer versions of air floor inflatables.

As JK says the keel inflation in particular will be critical at this size.... rechecked after a few mins on the water. Motor trim and load weight distribution might help a bit but the inflatable's design at this length is a huge factor.

I hope you get it sorted but it may just be a trade off for the fact that you can get seven Saturn 18s for one FC470.. something has to give in design/construction at that price difference.

[jeffstevens763@g]

as above make sure the fabric which forms the hull is ridgid that prevents air getting trapped causing the hull to go concave.

[nmzodiac]

I’ll try upping the keel pressure today and let you all know if it works.
Thanks

[Pikey Dave]

Am I the only one that thought this was about the "Mile High" club when I saw the title[emoji15]

[willk]

Originally Posted by Pikey Dave

Am I the only one that thought this was about the "Mile High" club when I saw the title[emoji15]

Maybe not.

Apparently I haven't yet gone entirely feral. Gimme a month...

[Yabadabadoo]

Originally Posted by Pikey Dave

Am I the only one that thought this was about the "Mile High" club when I saw the title[emoji15]

Nope, I thought sounds like a perfect set up to me [emoji23]

[spartacus]

Originally Posted by Pikey Dave

Am I the only one that thought this was about the "Mile High" club when I saw the title[emoji15]

Classic case of watching too many Carry On films during the 70s.

https://m.youtube.com/watch?v=ejm2e5bxxcc

[nmzodiac]

Hmmm I am sailing at over 5000 feet above sea level. Does that count [emoji41]

[Pikey Dave]

Originally Posted by spartacus

Classic case of watching too many Carry On films during the 70s.

Fnaaar fnaaar snigger snigger[emoji12]

[jeffstevens763@g]

Originally Posted by Pikey Dave

Am I the only one that thought this was about the "Mile High" club when I saw the title[emoji15]

Nope thought door was open

[nmzodiac]

I upped the keel and tube pressure still have the same sensation I guess it is just the limitation of the boat.
Thanks for the ideas and the [emoji23][emoji38][emoji5]

[jeffstevens763@g]

Originally Posted by nmzodiac

I upped the keel and tube pressure still have the same sensation I guess it is just the limitation of the boat.
Thanks for the ideas and the [emoji23][emoji38][emoji5]

tell us more what pressures have you got,hp of motor and set up might be something not quite right

[nmzodiac]

Originally Posted by jeffstevens763@g

tell us more what pressures have you got,hp of motor and set up might be something not quite right

Hey Jeff
It’s a 18 foot boat
Main tubes are at ~3.8 PSI
Keel is at ~ 4.5 PSI
Running an old 70hp 2 stroke Evinrude maybe putting out 50 hp with the age and altitude I’m running it at 5000 feet above sea level. Motor weighs 195 lbs
Running a 16 pitch prop the boat seems to like 4K rpm at 22 mph

I have two seats mounted in front of the jockey seat (see attached picture). Wife is usually in one of the front seats

Combined passenger and stuff weight is ~ 350 - 400 lbs

Thanks
Adrian

[jeffstevens763@g]

https://www.tirerack.com/tires/tiret...jsp?techid=167
Hi Adrian

Could it be pressure drop at altitude the table above is tire pressure differences about 2psi at 5000 feet nice boat by the way
is this the boat adrian below
https://www.saturnboats.com/inflatab...turn-boat.html

[jeffstevens763@g]

ignore the pressure drop it would over inflate from sea level to altitude senior moment,

does the bimi top make a difference when its down eg; more or less lift

[cgoing]

Run many boats without speed tubes , Achilles, Avons , Zodiacs to name a few and never experienced what you are describing.

[nmzodiac]

Originally Posted by jeffstevens763@g

https://www.tirerack.com/tires/tiret...jsp?techid=167
Hi Adrian

Could it be pressure drop at altitude the table above is tire pressure differences about 2psi at 5000 feet nice boat by the way
is this the boat adrian below
https://www.saturnboats.com/inflatab...turn-boat.html

Yes that’s the boat.

[yowsa52]

I am getting the same with SD385. Keel is at 6psi but I am going to go up to 8psi and fully inflate floor to 13-15psi next outing in a couple of days.