Small Rib advice

[5teve]

Hi Guys

My old Zodiac 2.6m fiberglass hulled rib tender has started to die (fall to pieces) so today I bought a 2.6m aluminum hulled rib and 5hp Mercury (tohatsu) 2 stroke - used. The Motor is 1 hour old (long story) and the rib is about 5 years but in good condition. The rib has a very deep V especially at the front.. I went aluminium for the weight saving over the zodiac to ease the handling as the old zodiac is around 50+kg..

I took it for a spin between swapping tenders over on the boat and noticed it runs VERY bow high.. even if I sit as far forward as I can.. (17st) it still is bow high. It gets up on the plane and shifts (its only 33kg hull weight) but I'm feeling its too high. I messed with the trim pin.. it was on the second from then transom so moved it to the closest and it didnt seem to make much difference, so I am wondering what else it could be...

I have no idea on the cav plate location.. in relation to the hull bottom.. as I didnt check it before hauling the boat on board (I was short of time) but I did notice some side spray coming off the motor going over the tube end on one side only.. but I thought that was because the bum was buried with the nose high..

Anyway as usual - thoughts appreciated.. i'll be cleaning the tubes over the next few days and then coating them with some kind of UV protection.. then I'll get it back in the water and see what we can do..

Steve

 

[gordmac]

Maybe that is just how the hull design works? Could you fit some sort of trim tabs?

 

[Rocksteadee]

Hi Guys

My old Zodiac 2.6m fiberglass hulled rib tender has started to die (fall to pieces) so today I bought a 2.6m aluminum hulled rib and 5hp Mercury (tohatsu) 2 stroke - used. The Motor is 1 hour old (long story) and the rib is about 5 years but in good condition. The rib has a very deep V especially at the front.. I went aluminium for the weight saving over the zodiac to ease the handling as the old zodiac is around 50+kg..

I took it for a spin between swapping tenders over on the boat and noticed it runs VERY bow high.. even if I sit as far forward as I can.. (17st) it still is bow high. It gets up on the plane and shifts (its only 33kg hull weight) but I'm feeling its too high. I messed with the trim pin.. it was on the second from then transom so moved it to the closest and it didnt seem to make much difference, so I am wondering what else it could be...

I have no idea on the cav plate location.. in relation to the hull bottom.. as I didnt check it before hauling the boat on board (I was short of time) but I did notice some side spray coming off the motor going over the tube end on one side only.. but I thought that was because the bum was buried with the nose high..

Anyway as usual - thoughts appreciated.. i'll be cleaning the tubes over the next few days and then coating them with some kind of UV protection.. then I'll get it back in the water and see what we can do..

Steve

The cavitation plate should sit around an inch +, lower than the bottom of the keel when looked along the length of the keel
The trim with the pin closest to the transom will give the bow lowest attitude as the prop will giving some thrust downwards by a small degree.

Is the boat planning? As it sounds like it might be trying to climb out of the hole. 17st at the back may not be helping as it would hold the stern down and 5 hp may not be big enough

 

[Hambleite]

Assuming she is actually planing, does she ride at consistent attitude when at WOT?

Or does she porpoise up and down?

I guess if the ride is at a consistent attitude when WOT then that is probably how she flies!

A deeper V hull will tend to give a more bow up attitude when planing, especially compared to a more flat bottomed hull shape.

 

[Beamishken]

The cavitation plate should sit around an inch +, lower than the bottom of the keel when looked along the length of the keel
The trim with the pin closest to the transom will give the bow lowest attitude as the prop will giving some thrust downwards by a small degree.

Is the boat planning? As it sounds like it might be trying to climb out of the hole. 17st at the back may not be helping as it would hold the stern down and 5 hp may not be big enough

If you set the engine 1"low you will have masses of spray off the leg and it will limit the performance due to extra drag the extra deep prop will also be trying to push the bow up.
Set the engine approximately 1"up from keel line.
We have a ribeye aluminium tender & find its deeper vee a different ride to our previous airdeck tender. Its all about weight distribution . If your using the boat alone it may be worth investing in a tiller extension so you can get further forward. The bow will sit a little higher than your air deck as its a deeper vee but once your used to the difference id imagine you will find it to perform better and handle better than the air deck. Ours is far better

 

[Rocksteadee]

If you set the engine 1"low you will have masses of spray off the leg and it will limit the performance due to extra drag the extra deep prop will also be trying to push the bow up.
Set the engine approximately 1"up from keel line.
We have a ribeye aluminium tender & find its deeper vee a different ride to our previous airdeck tender. Its all about weight distribution . If your using the boat alone it may be worth investing in a tiller extension so you can get further forward. The bow will sit a little higher than your air deck as its a deeper vee but once your used to the difference id imagine you will find it to perform better and handle better than the air deck. Ours is far better

 

[5teve]

Maybe that is just how the hull design works? Could you fit some sort of trim tabs?

Trim Tabs wouldnt be an option on this.. although I could fit them.. it would be a bit silly I think... i could put some form of interupter on instead though... this would be a last resort..

The cavitation plate should sit around an inch +, lower than the bottom of the keel when looked along the length of the keel
The trim with the pin closest to the transom will give the bow lowest attitude as the prop will giving some thrust downwards by a small degree.

Is the boat planning? As it sounds like it might be trying to climb out of the hole. 17st at the back may not be helping as it would hold the stern down and 5 hp may not be big enough

Its actually 17st at the front.. on the front of the bench seat reaching back!

I have to check the motor length.. i was pushed for time yesterday... but will ensure i check how it is set up.. problem is I cannot adjust the height when it is a clamp on motor.. not without some kind of extension to the transom..

I think its planing when I lean forward... but it still feels high.. it could be the case its a lot higher (to to the fine entry) at the front than i'm used to.. so may be just me needing to get used to it.

Assuming she is actually planing, does she ride at consistent attitude when at WOT?

Or does she porpoise up and down?

I guess if the ride is at a consistent attitude when WOT then that is probably how she flies!

A deeper V hull will tend to give a more bow up attitude when planing, especially compared to a more flat bottomed hull shape.

No porpoising as such.. and yes fairly consistent.. it just feels as though a good gust of wind may flip it up!

If you set the engine 1"low you will have masses of spray off the leg and it will limit the performance due to extra drag the extra deep prop will also be trying to push the bow up.
Set the engine approximately 1"up from keel line.
We have a ribeye aluminium tender & find its deeper vee a different ride to our previous airdeck tender. Its all about weight distribution . If your using the boat alone it may be worth investing in a tiller extension so you can get further forward. The bow will sit a little higher than your air deck as its a deeper vee but once your used to the difference id imagine you will find it to perform better and handle better than the air deck. Ours is far better

View attachment 80386

I was thinking an extension just for solo journeys.. probably need to find out how it goes 3 up.. but yes its different to our fibreglass hull one.. mind you that only had a 2.5hp on so couldnt plane! As mentioned I cant adjust the height without building the transom so it may just be the way it is.. may have to invest in some lead I will check the height out and see what shaft length motor I have...

Thanks for the replies so far guys

Steve

 

[Rocksteadee]

Could you get someone to video you?
If you have Navionics on your phone, thus can give you your speed. I would guess that you would have to be about 8 it’s to be planing.
A tiller extension would help to get weight further forward

 

[Beamishken]

The usual method of lifting a clamp on engine is to sit the engine on a wood batten the required thickness laid along the top of the transom. Obviously you can only go up around 25 or 30mm before you run out of space for the clamps to grip but thats often enough.
The tel tail sign of the engine being too low are lots of spray shooting off to each side or upwards to the power head or the av plate being completely buried when on the plane.

 

[Greg2]

Whilst I stand to be corrected I would be surprised if a 2.6m RIB fitted with a 5hp engine manages to get on the plane properly with a 17st bloke in it no matter where you sit. I am a similar size and have had several RIBs in the 2.7 to 3.1m bracket (hulls in GRP, ali and airdeck) and have always had a 10hp to get any kind of decent performance. It sounds to me like it is not getting fully on the plane and a larger motor may well flatten things out as the stern lifts properly onto the plane.

 

[Ferris]

Any way of determining engine revs at WOT? Prop may not be letting the engine get into it power band - common enough issue for small RIB's and SIB's. I have an old Zodiac 3.1 with 8hp Honda and that does 18kts with two people so I'd imagine a much lighter RIB and engine combo should plane. Also, put the fuel tank up the bow, every little bit helps.

 

[longjohnsilver]

Whilst I stand to be corrected I would be surprised if a 2.6m RIB fitted with a 5hp engine manages to get on the plane properly with a 17st bloke in it no matter where you sit. I am a similar size and have had several RIBs in the 2.7 to 3.1m bracket (hulls in GRP, ali and airdeck) and have always had a 10hp to get any kind of decent performance. It sounds to me like it is not getting fully on the plane and a larger motor may well flatten things out as the stern lifts properly onto the plane.

That’s what I was thinking. I have an Avon 2.8 with a 15hp, with just 2 of us it takes a bit of effort to plane.

I just think 5hp is not enough.

 

[Beamishken]

We have a 2.8 aluminium hull tender it planes fine with 2 adults and a 3 year oldwith an 8hp, it previously had a 5hp yam 2 stroke and it would plane with 1 adult and child even with a 17 stone passenger it should plane although I'd admit it is on the limit. maybe a set of dole fins would give it the little extra lift in the stern it needs

 

[QBhoy]

Not sure where that advice on engine set up came from but it’s wrong.

Anyway. I’m thinking that maybe your new rib is shorter than the old ? Shorter hulls do this.
I had a 3m valiant rib that would plane easily with 2 onboard and an 8hp Yam 2 stroke.
The same engine on a 2.7m brigg and 2 onboard wouldn’t plane. Despite being lighter.

 

[Fishtigua]

I had a 2.3 rib from Tohatsu with a 15hp Yam. The bow stood up so far I used to stand right at the bow, holding the painter, with a long tiller extention and kill cord.

After bombing around Herm and Sark like this, decided to fit a pair of dolphin fins to the trim plate. Cheap, simple and made all the difference.

 

[Restoration man]

I’ve got 2.7 walker bay rib with 5hp mercury 2 stroke and that planes and I’m 14stone 6 lbs

 

[5teve]

Could you get someone to video you?
If you have Navionics on your phone, thus can give you your speed. I would guess that you would have to be about 8 it’s to be planing.
A tiller extension would help to get weight further forward

I thought about a tiller extension but thought I would add the family first - just have to wait for that to happen.. I should be able to get speed no problem. It felt faster than 8 kts.

The usual method of lifting a clamp on engine is to sit the engine on a wood batten the required thickness laid along the top of the transom. Obviously you can only go up around 25 or 30mm before you run out of space for the clamps to grip but thats often enough.
The tel tail sign of the engine being too low are lots of spray shooting off to each side or upwards to the power head or the av plate being completely buried when on the plane.

I have measured the engine / hull - hull is for short shaft - which is what it is.. so transom is approx 410mm (directly along it) to the keel bottom (only small) and the engine is about 435mm to bottom of cav plate. A small lift may make a difference but I'll need to remove the clamp pads etc to block it up.

Whilst I stand to be corrected I would be surprised if a 2.6m RIB fitted with a 5hp engine manages to get on the plane properly with a 17st bloke in it no matter where you sit. I am a similar size and have had several RIBs in the 2.7 to 3.1m bracket (hulls in GRP, ali and airdeck) and have always had a 10hp to get any kind of decent performance. It sounds to me like it is not getting fully on the plane and a larger motor may well flatten things out as the stern lifts properly onto the plane.

You could well be right.. but it felt like it was trying - motor isnt run in yet.. (not even used one tank) so being a bit careful but it felt like it wasnt struggling - the RIB is only rated to 5hp.. as its only a 2.6m..

Any way of determining engine revs at WOT? Prop may not be letting the engine get into it power band - common enough issue for small RIB's and SIB's. I have an old Zodiac 3.1 with 8hp Honda and that does 18kts with two people so I'd imagine a much lighter RIB and engine combo should plane. Also, put the fuel tank up the bow, every little bit helps.

I'm looking at adding an inductive tach.. cheap and easy.. so should be able to sort something out. Fuel tank is 2.5ls and is in the engine cowling..

That’s what I was thinking. I have an Avon 2.8 with a 15hp, with just 2 of us it takes a bit of effort to plane.

I just think 5hp is not enough.

Thanks - that is what I am trying to find out. I assume the avon is soft bottomed? also a bit more than 30kg?

We have a 2.8 aluminium hull tender it planes fine with 2 adults and a 3 year oldwith an 8hp, it previously had a 5hp yam 2 stroke and it would plane with 1 adult and child even with a 17 stone passenger it should plane although I'd admit it is on the limit. maybe a set of dole fins would give it the little extra lift in the stern it needs

Thanks - I'm looking at the fins as an option - just want to ensure i'm covering all bases.

Not sure where that advice on engine set up came from but it’s wrong.

Anyway. I’m thinking that maybe your new rib is shorter than the old ? Shorter hulls do this.
I had a 3m valiant rib that would plane easily with 2 onboard and an 8hp Yam 2 stroke.
The same engine on a 2.7m brigg and 2 onboard wouldn’t plane. Despite being lighter.

Old rib and new are same - old rib had a 2.5hp 4 stroke - and that wouldnt plane.. very sedate - the rib was over 50kg too.. and a lot flatter hull than the new..

I had a 2.3 rib from Tohatsu with a 15hp Yam. The bow stood up so far I used to stand right at the bow, holding the painter, with a long tiller extention and kill cord.

After bombing around Herm and Sark like this, decided to fit a pair of dolphin fins to the trim plate. Cheap, simple and made all the difference.
View attachment 80420

wow - 2.3m rib with a 15hp.. sounds like fun.. yep looking at the fins once I know I have covered all bases..

I’ve got 2.7 walker bay rib with 5hp mercury 2 stroke and that planes and I’m 14stone 6 lbs

Good to know.. what weight is the rib and what hull?

So I have the measurements so it looks like the engine is probably low but marginal.

While cleaning its is noticeable how much higher at the front it is that the old zodiac - so it could also be me not being used to it and thinking its high bow running when in fact its just the tubes being high at the front. I'll try and get some pictures over the next few days of the hull and boat in general.

Will update soon

Steve

 

[Lulla-Belle]

Ive got exactly the same problem bought 2.9 Quicksilver Ali Lightweight hull for a tender as we beach a lot and we have massive tides here in the Bristol Channel hard work dragging anything back to the sea !

Boat plate clearly states 15Hp max so to be sure we purchased 10Hp - 43Kg well inside max 50Kg

Beach wheel fitted to the transom small grey ones, Im a large lad 16.5 stone and when I need to start engine etc my weight on the stern makes it so unsafe I can see it flipping backwards.

If i sit in the bow and my son operated it flies planes early etc but one person no chance!

Moved fuel tank up front etc just little peeved as I have a 4hp engine but wanted to have some fun in it?

Stuck between choices?? any advice to help it get up on plane with 10hp and crack on a bit appreciated.

Or have I been miss sold this engine rib comb?

Love the rib its great build quality etc

I have a sea-rider with a 115hp that flies but wont fit in the Targas Garage!!!

TIA!

 

[longjohnsilver]

No the Avon is a grp rib.

 

[rlw]

Ive got exactly the same problem bought 2.9 Quicksilver Ali Lightweight hull for a tender as we beach a lot and we have massive tides here in the Bristol Channel hard work dragging anything back to the sea !

Boat plate clearly states 15Hp max so to be sure we purchased 10Hp - 43Kg well inside max 50Kg

Beach wheel fitted to the transom small grey ones, Im a large lad 16.5 stone and when I need to start engine etc my weight on the stern makes it so unsafe I can see it flipping backwards.

If i sit in the bow and my son operated it flies planes early etc but one person no chance!

Moved fuel tank up front etc just little peeved as I have a 4hp engine but wanted to have some fun in it?

Stuck between choices?? any advice to help it get up on plane with 10hp and crack on a bit appreciated.

Or have I been miss sold this engine rib comb?

Love the rib its great build quality etc

I have a sea-rider with a 115hp that flies but wont fit in the Targas Garage!!!

TIA!

Lulla-Belle do you have the Targa 52? . Would be interested to know if the a 290 rib fits with it's engine on? Also looking for a small rib in the T52