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  1. #1
    Join Date
    Feb 2016
    Location
    Western Australia
    Posts
    203

    Default Small Rib advice

    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

  2. #2
    Join Date
    Jan 2009
    Location
    Lochaber
    Posts
    7,252

    Default Re: Small Rib advice

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

  3. #3
    Join Date
    Jul 2011
    Posts
    451

    Default Re: Small Rib advice

    Quote Originally Posted by 5teve View Post
    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

  4. #4
    Join Date
    Jan 2017
    Posts
    39

    Default Re: Small Rib advice

    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.

  5. #5
    Join Date
    Dec 2001
    Location
    north ayrshire
    Posts
    464

    Default Re: Small Rib advice

    Quote Originally Posted by Rocksteadee View Post
    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

  6. #6
    Join Date
    Jul 2011
    Posts
    451

    Default Re: Small Rib advice

    FC338100-7450-465D-B498-5670544298A5.jpeg

    Quote Originally Posted by Beamishken View Post
    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

  7. #7
    Join Date
    Feb 2016
    Location
    Western Australia
    Posts
    203

    Default Re: Small Rib advice

    Quote Originally Posted by gordmac View Post
    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..

    Quote Originally Posted by Rocksteadee View Post
    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.

    Quote Originally Posted by Hambleite View Post
    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!

    Quote Originally Posted by Beamishken View Post
    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
    Quote Originally Posted by Rocksteadee View Post
    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

  8. #8
    Join Date
    Jul 2011
    Posts
    451

    Default Re: Small Rib advice

    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

  9. #9
    Join Date
    Dec 2001
    Location
    north ayrshire
    Posts
    464

    Default Re: Small Rib advice

    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.

  10. #10
    Join Date
    Jun 2002
    Posts
    2,819

    Default Re: Small Rib advice

    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.

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