New 6 meter sib and problems

[SixtyNorth]

If I remember correctly, all the Zodiac Milpro inflatable boats over about 4.7m in length have a trimaran hull design with speed tubes. There may well be a good reason for this as they use the same design on their workboats as well as military spec. inflatables.
Large inflatable boats are generally designed and used for carrying very heavy loads rather than for high speeds. That being the case, if not carrying heavy loads, you may well be better off with a smaller and lighter engine or a RIB for your current outboard.

[spainman]

For me ir its a Big problem.

Some other manufacturas make the sibs on this class without speed tubes this could not be the reason.

Like narwhal or DsB .

The speed is now secondary.

The problem is the ventilación or cavitation or what ever it is.

The rpm increase and boat do not go forward.

The mecánic told the motor could No be the problem.
It is by ce certificación for 90 HP máximum.
Maybe a fabricación. Error ? But where ?

When the waves come infront of the boat It is better

tested the waves coming from back It was terrible

I must know what hapoens and resolve It.

[spainman]

The aluminium floor has sides stringers and is well joined together.

What i just observes ls the front of the boat if you lock at the picture i put un the thread the front is like on the same level as the total boat. The keel just lift It Up.

Un other sibs the front nose goes Up.

[Steve509926]

Hola España hombre, no se si te estas tomando el pelo o no. Hay muchas inconsistencias en tu hilo. ¡Primero dices que lo compraste hace un mes, luego dices que lo compraste hace ocho meses! ¿Cuál es?

[spainman]

I bought it last year but du to pandemig i fit motor and launched it just some weeks ago.

I do not habe to ley. I just looking for help

So please do not wright thinks like that which do not help me.

[spainman]

Has anybody more ideas to test ?
I write an email to the chinese fábric yesterday.

[Steve509926]

Originally Posted by spainman

I bought it last year but du to pandemig i fit motor and launched it just some weeks ago.

I do not habe to ley. I just looking for help

So please do not wright thinks like that which do not help me.

Just checking

Seriously though, I think you have been given some good advice on here.

First and foremost, as suggested by others, I would try a smaller, lighter outboard around 30hp.
If you get max RPM, a decent speed with little ventilation, then your current OB may be to heavy for your sib.

I know you said your sib is rated to 90hp but it should have a maximum OB weight on the transom plat. Is your 60 hp Parson below that weight?

[paintman]

What is the exact make & model of your sib?
All I can find you saying so far is "It is an chinese modell but of a goog builder and with mehler pvc."

Have you tried searching the internet to see if others have had problems with that boat?

[Fenlander]

>>>Has anybody more ideas to test ?

I think in the 47 posts above... and trying different props and trim settings with your mechanics... you've had about every idea there is and most of us seem to be of the opinion that SIB is not well enough designed/built for such a heavy motor and that horsepower.

If it were mine I'd try and borrow a lighter 30/40hp motor and give it a go just on the tiller to see how that changes things. Beyond that I'd keep the engine and sell the SIB then look for a used RIB to suit the 60hp that needs a new engine.

I'm not sure you are ever going to be really happy with your current outfit.

[TmMorris]

Originally Posted by spainman

Has anybody more ideas to test ?
I write an email to the chinese fábric yesterday.

You need to test the hill with different motors. That's your first step. Ultimately, you want to test it with another 60 then a smaller engine and then a larger. You want to collect a dataset that categorically confirms that it is not the engine but the boat. You could even try a long shaft outboard at the same time.

At which point you need to open a proper dialog with the company that sold it to you. Step 1 of this would be to establish from the manufacturer their performance claims. You need the manufacturer to tell you, in writing, what the performance capabilities of the hill are if you had not already established this prior to purchase.

With the data that proves the engine is not the issue and the information from the manufacturer you then begin the process of exercising your consumer rights with the vendor. Because you have two simple choices which is that you either live with the fact that an enormous 6m piece of rubber that has to be pushed through the water is not going to have a top speed anywhere close to something with an actual hull that can climb out into the plane. Or you utilise your rights to return the goods and take your money back.

Contemplating cutting the transom is nothing short of daft. The engine sounds absolutely fine and if you've now inflated all sections of the boat correctly then 99.99% for sure you have a boat that has so much drag due to those long tubes never getting out of the water that 20 knots is what you're going to get whatever you do.

The question to be asking yourself about 6m SIBs is what are the designed for? Our SIBs are not exactly performance designs. Their value lies in their massive storage and cost advantage. The shorter they are the more of the tube area gets lifted out of the water by the simple and shallow hill design.

What's the purpose of a 6m SIB? It's not powerboat racing or any kind of speed performance because our SIBs have terrible performance crippling inherent characteristics and these get amplified the longer the design becomes. At 6m you essentially have an enormous floppy sausage that you're attempting to push through custard by blowing in it.

So did the manufacturer of your boat design it to hit 30+ knots or is a 6m SIB primarily designed to be the cheapest way to transport a load of objects across a body of water at 20 knots? Is the ability to take a 90hp outboard so that one bloke can hit 40 knots or so that 8 blokes with kit can hit 20 knots?

I suspect the power of your engine isn't there for top speed but to get a heavy load onto the plane.

Seeing as you've opted for a massive 6m boat I assume you have a lot of stuff to be transporting somewhere and done on a tight budget so surely the boat is ideal as with that 60hp outboard you'll be able to get it on the plane even with a big load?

[spainman]

To explain.
I have no havy weights to carry and i had ribs before and currently a 29 starfisher cancun.

This was like a small dream because as i was young we had a zodíac mk V in our family and with an old 100 hp Mercury and it was so cool when i could drive as an passanger on it.

So i wanted to have something similar.
I repead that after all readint inunderstand that the speed will be more. But i need to solve the problem with the rpm which make the boat stop and decrease the speed and increase just rpm like i will jumping on waves with the only diference that I am not and that the motor shaft is not outside the water.

[spainman]

The manufacturer is a very known one.

Quingdao linya boats and the model is ub 600

[Steve509926]

Originally Posted by TmMorris

You need to test the hill with different motors. That's your first step. Ultimately, you want to test it with another 60 then a smaller engine and then a larger. You want to collect a dataset that categorically confirms that it is not the engine but the boat. You could even try a long shaft outboard at the same time.

At which point you need to open a proper dialog with the company that sold it to you. Step 1 of this would be to establish from the manufacturer their performance claims. You need the manufacturer to tell you, in writing, what the performance capabilities of the hill are if you had not already established this prior to purchase.

With the data that proves the engine is not the issue and the information from the manufacturer you then begin the process of exercising your consumer rights with the vendor. Because you have two simple choices which is that you either live with the fact that an enormous 6m piece of rubber that has to be pushed through the water is not going to have a top speed anywhere close to something with an actual hull that can climb out into the plane. Or you utilise your rights to return the goods and take your money back.

Contemplating cutting the transom is nothing short of daft. The engine sounds absolutely fine and if you've now inflated all sections of the boat correctly then 99.99% for sure you have a boat that has so much drag due to those long tubes never getting out of the water that 20 knots is what you're going to get whatever you do.

The question to be asking yourself about 6m SIBs is what are the designed for? Our SIBs are not exactly performance designs. Their value lies in their massive storage and cost advantage. The shorter they are the more of the tube area gets lifted out of the water by the simple and shallow hill design.

What's the purpose of a 6m SIB? It's not powerboat racing or any kind of speed performance because our SIBs have terrible performance crippling inherent characteristics and these get amplified the longer the design becomes. At 6m you essentially have an enormous floppy sausage that you're attempting to push through custard by blowing in it.

So did the manufacturer of your boat design it to hit 30+ knots or is a 6m SIB primarily designed to be the cheapest way to transport a load of objects across a body of water at 20 knots? Is the ability to take a 90hp outboard so that one bloke can hit 40 knots or so that 8 blokes with kit can hit 20 knots?

I suspect the power of your engine isn't there for top speed but to get a heavy load onto the plane.

Seeing as you've opted for a massive 6m boat I assume you have a lot of stuff to be transporting somewhere and done on a tight budget so surely the boat is ideal as with that 60hp outboard you'll be able to get it on the plane even with a big load?

Bloody hell Tim, I've been to Helford and back from Mylor in less time than it took me to read that

The phrase horse, water, lead springs to mind!

[Steve509926]

Hi Spainman, whilst I was packing away my SIB this morning I had a thought.
Do you have a bilge pump fitted? Is the bilge so full of water and so heavy that it's pinning your sib down so that it can't drain out?

[spainman]

No no bilge pump
No water

[spainman]

Slowly we are coming forward.

So. the chinese Fabric respond very quickly that my problem is an isolatete one and they have never heard something like that. told that it is maybe the prop ( the gum inside)

I have told tham that this is not posible, because we tested 2 new props and result the same.

I have send some photos of the transom bracket and mounting on the motor and they will respond.

I also called and written to my dealer in Spain, he passed me to his mecanic who has mounted some ones and have told me that in the past they have cut some transom bracket a bit because of similiar problems with outher sibs of this fabric but a bit smaller. a 6 meter he never tought.

He told me this is because for example the Yamaha Endura 2 strokes engines the shaft lengh in L size for example is longer and the cavitation plate if you mount it normal is more down, under the bottom of the hull, because it is a SIB and not a Rib, it is different he told me.

I will wait what the fabric will tell me but maybe this is the problem.

I will inform when i have notice, good or bad.

[jeffstevens763@g]

Originally Posted by spainman

Thank you for your good answer.

I have the following prop: original: 11 1/2- 13
other I bought to test: 11 3/4 -12

My problem is the following:

The first 10-15 minutes I reach this 22 knots with GPS, but after giving full throttle it goes down.

Up to 3.000 rpm giving slowly throttle their is an forward going, after RPM goes up and no forward.

This happens with both props.

Their must be something wrong.

Now I can just giving slowly throttle up to 3.000 rpm and after RPM goes up and the boat go slowlier.

The mecanic will come next week to make a testdrive.

I had some sibs before ( smaller ) and newe has this problem.

Zodiac and some other Manufactures make SIb´s with 6,7,8 meters.

You have about 100 rpm difference between your two props so virtually the same so your test means you are at 4900 rpm max and the props too high geared an inch of diameter is equivalent to 200 rpm and an inch of pitch equivalent to 150 rpm ish you need to get to around 5500 rpm plus IMO assuming everything else is correct

[spainman]

Update.

So the nautic store has cut me 6 cm in the transom plate of the Boat and now their is no cavitation.

I will put it One cm higher and see if still ok.

But the problem is solved with this.

I will start a new thread because I am looking for something quicker