Zodiac acti V not planning

BCRyan · 24 May 2021, 22:40

Hi All,
I have a Zodiac Cadet 325 Fastroller ACTI-V with a new Tohatsu 9.8 4 stroke by myself she planes no problem but is anyone is in the boat with me I cannot get her to plane, floor and tubes checked multiple time to ensure proper inflation. I have tried shifting weight a number different ways and nothing, even put hydrofoils on the motor with no change. Tried every trim angle on the motor too.

I notice the floor bows up a lot in the back 3ft of the boat and that must be hurting it’s chances to get on plane so I was thinking of cutting plywood and wedging between airfloor and pontoons that covers the back 3ft and see if it will hold the floor down and make the boat plane.

Or I was thinking maybe trim tabs on the transom could fix the issue.

Anyone have any suggestions? Was very disappointed when out on the lake with the family and not being able cruise across the lake. Love the stability of the zodiac but need it to plane because it’s too much stress on the motor pushing all that water.

Thanks for any advice

Fenlander · 24 May 2021, 23:25

I've only had the 3.4 and 3.6m versions of that boat and ran them with 15hp motors but applying my experience with 10hp motors on other SIBs I'd say you should plane two up as long as either/both is average weight.

The floor flex under power is an issue to a degree but it shouldn't prevent getting on the plane just cause occasional prop slip once on the plane. Are you 100% sure your gauge is accurate and you have tubes and floor right up to pressure and rechecked after the air cools a little?

BCRyan · 24 May 2021, 23:37

I am pretty sure the pressure was right but I am assuming the gauge was correct, and even tried over inflating to see if that would help. I guess I should try another gauge to be sure. Max HP in this boat is 10hp so I figured 9.8 would pop this up and fly on the lake was pretty surprised when it felt like I was towing an anchor thru the water.

Limecc · 25 May 2021, 00:07

You ought to have seen at least some difference with the Doel (maybe this is the rearmost lift you describe?) but suspect you need a different prop when fully loading the boat.

Why not get a prop one or two sizes down? At higher revs it develops more power and you stand a chance of planing.

With such a small motor I don't think one size will fit all, I'm even struggling with this with 50hp. Slow to get up with four, then bouncing off the rev limiter when alone.

Also when you do get it planing, without a tach you are operating in the dark so you might consider one of those.

Btw I don't think trim tabs will help much at displacement speed, the hydrofoil is a much better way of getting stern lift and should help, but your basic problem is too much drag (ie too low in the water) and not enough power to get over the hump.

BCRyan · 25 May 2021, 00:14

I do have a tach I installed on the motor and I’m getting to about 5700rpm at full throttle when on plane by myself, max recommended rpm is 5000-6000 on this motor so that seems about right.
If I add 150lbs person max rpm is 4700 rpm and won’t plane.

Concerned if I try a different pitch prop to help plane with 2 people it will really mess things up when I’m solo in the boat.

Fenlander · 25 May 2021, 00:15

Good reminder re prop pitch.

I'm assuming a standard 8.5" or so which should be fine but check and see what you have fitted. The floor bowing up towards the transom is classic air floor problem at its worse.

BCRyan · 25 May 2021, 00:36

Yes it is the 8.5 prop

Limecc · 25 May 2021, 00:46

Quote:

Originally Posted by BCRyan

Concerned if I try a different pitch prop to help plane with 2 people it will really mess things up when I’m solo in the boat.

No way around it.
"Ye cannae change the laws of physics capn!"

Maybe you could fit a bigger carb or something though.

Maximus · 25 May 2021, 07:47

Quote:

Originally Posted by Limecc

No way around it.
"Ye cannae change the laws of physics capn!"

Maybe you could fit a bigger carb or something though.

More power.... or less weight!

paintman · 25 May 2021, 09:04

Quote:

Originally Posted by BCRyan

I do have a tach I installed on the motor and I’m getting to about 5700rpm at full throttle when on plane by myself, max recommended rpm is 5000-6000 on this motor so that seems about right.
If I add 150lbs person max rpm is 4700 rpm and won’t plane.

Concerned if I try a different pitch prop to help plane with 2 people it will really mess things up when I’m solo in the boat.

Therein lies the problem.

You need to get everything set up for best performance with your 'normal' load.

Changing that load - lighter or heavier - will affect the performance & other than setting it all up again for best performance with this new load there's not a lot you can do.

In a car you simply select the appropriate gear but that's not an option with a boat.

Changing your prop will probably restore your loaded performance but when solo you'll over-rev at WOT. May not do a lot for your fuel consumption either.
Was it jonP who said he used to change props according to load?

Limecc · 25 May 2021, 09:17

Quote:

Originally Posted by paintman

Was it jonP who said he used to change props according to load?

Or even according to altitude.
Engines produce less power at high elevations, don't normally come across this though.

Swopping the prop's not too time consuming or difficult, and it's useful to have a get-you-home spare should one get damaged.

If you go one pitch down, you will still be under 6000rpm solo and might just get into WOT range when two up. Probably a 7p would be best.

Oldman2 · 25 May 2021, 09:19

Lake Titicaca anyone....

chipko · 25 May 2021, 09:51

Also think going down a pitch in props worth a punt.

As only pulling 5700 at wot you’re not exactly under propped at the moment even solo. Going down an inch to 7.5 should give around another 200rpm solo and might enable motor to get well into wot range when two up. It may even be no slower solo.

We tend to run slightly under propped with motor easily able to bounce off the limiter when solo, but giving good hole shot and still easily able to plane when loaded.

Agree ‘Mexican Wave’ bubble in floor also needs addressing.

BCRyan · 26 May 2021, 01:35

Thanks for all the suggestions since I do has some rpm to play with I think I will try a different prop size and see if that helps.

I have some other guys in another forum suggesting to try trim tabs either the nautiicus smart tabs or the maxi-marine lifters. I’m being told that these tabs really make a huge difference in helping to get up on plane.

Anyone have experience with these?

Thanks again

Limecc · 26 May 2021, 06:18

Quote:

Originally Posted by BCRyan

I’m being told that these tabs really make a huge difference in helping to get up on plane.

Anyone have experience with these?

No. Aren't they made for rigid hulls? You have a bendy floor SIB. You don't need extra stern lift, you already complained about it.

The former are designed to work at speed, and while the latter might make your boat plane more like the 3.4m sibling, they won't add bouyancy and you still have to live with a flexing hull. Imho if a 7" prop doesn't deliver I'd be swopping to a f-rib, you have the wrong boat.

Fenlander · 26 May 2021, 08:14

I appreciate all the stuff about prop changes and tabs/foils but the thing is from my experience of SIBs 3m-3.6m with various 9.8 motors this Zodiac should plane easily two up and make about 15kts.... all on a standard prop with a people/kit load totalling around 430lbs.

But it seems massive floor deflection and hooking is stopping that. I've never experienced this with the four Acti-V/Fastroller SIBs I've owned.. they all went on the plane easily and if there was ever bad behaviour from the air floor it was when already on the plane and seeking to speed up even more when the floor undulation and loss of grip happened.

Puzzling and I'm still drawn back to the issue of pressure. I'd be wondering about trying a gauge you could check somehow against a known pressure... and making sure you have the correct info on inflation pressures... what are they given as for this Zodiac?

Limecc · 26 May 2021, 08:39

Quote:

Originally Posted by BCRyan

even tried over inflating to see if that would help.

Quote:

Originally Posted by Fenlander

Puzzling and I'm still drawn back to the issue of pressure. I'd be wondering about trying a gauge you could check somehow against a known pressure... and making sure you have the correct info on inflation pressures... what are they given as for this Zodiac?

I agree it's hooking but didn't he already try extra pressure?

As you say, would be helpful to know the combined weights and inflation pressures involved. Is it one extra person or the entire family? I'm inclined to think it's overloaded.

@BCRyan, can you post a video?

Fenlander · 26 May 2021, 08:46

Yes he tried extra pressure but what if his gauge was a mile out and his extra pressure was still only 70% pressure. What if the info he was working to for pressures was wrong?

It's just as I've said above I have so much real life experience of this outboard hp on SIBs in the size range and what's happening to him is against all that.

rik_elliott · 26 May 2021, 09:01

Where is the second passenger sitting? You may need more weight in the bow to keep the nose down and pop it on to the plane. If they are sitting on the side midway down the boat or at the back you have no chance.

Are you measuring the floor pressure after inflating, or after putting the boat in the water for ten mins or so to cool the deck off? It makes an enormous difference to my honwave air deck and if I am in a rush and don't recheck and add air the deck bubbles up as you mention and the performance takes a hammering. Are you inflating using an electric pump or by hand? If can be nigh on impossible to hit working pressure manually.

I've had tons of inflatables and weight distribution and floor pressure are the culprits in almost every case of under performance. You can fix both these things for free.

Limecc · 26 May 2021, 09:05

Quote:

Originally Posted by Fenlander

Yes he tried extra pressure but what if his gauge was a mile out and his extra pressure was still only 70% pressure. What if the info he was working to for pressures was wrong?

It's just as I've said above I have so much real life experience of this outboard hp on SIBs in the size range and what's happening to him is against all that.

Agreed.
On my SIB I never used a gauge after I discovered the digital pump was accurate. Inflating that last bit by hand was a killer so that method didn't last long.

Quote:

Originally Posted by rik_elliott

Where is the second passenger sitting? You may need more weight in the bow to keep the nose down and pop it on to the plane.

He tried all manner of weight distribution and the bow is already down because it's bending. Good points like Fenlander's otherwise. Something's off.