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Old 02 December 2009, 05:49   #1
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Not fast enough

HELLO

I hava rib which wont go on the plene (sorry if thats not the correct word I am new to this)

It does if i am on it myself but with all my fishing gear it wont, I have bought another engine so I can have 2 on the back, they just fit but this is very hard to drive as it needs two hands.

Any help on how to make it go faster with just the one engine
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Old 02 December 2009, 06:31   #2
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How long is the boat? what engine(s) have you got atm?
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Old 02 December 2009, 06:32   #3
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Old 02 December 2009, 06:49   #4
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ATM?

Automated
Tiller
Mechanism?

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Old 02 December 2009, 07:05   #5
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I hava rib which wont go on the plene
Most airlines will now only accept ribs as checked excess baggage. Redbay are a refreshing exception to this rule with their exciting range of purpose built Cabin Ribs. Not to be confused with Osprey "Carry-On" ribs.
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I have bought another engine so I can have 2 on the back, they just fit but this is very hard to drive as it needs two hands.
I generally have very little trouble with my twins. You should check that both engines are in the same gear. If the new engine was manufactured in the Southern Hemisphere, it may be running in reverse due to the influence of Coriolis Forces on the metal forging process.

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Old 02 December 2009, 07:20   #6
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More iformation required i see.

My rib is 3.1M and my main engine is a Susuki 6hp 4stroke my other engine is a Johnston 6hp 4 stroke but it looks identical except for the colour of course,

I think the extra weight on the back might cause a problem but it think there might be something else as i woiuld have thought 2 would be twice as fast.
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Old 02 December 2009, 07:34   #7
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On a more serious note......

I'm guessing you have an inflatable keel'ed hull as opposed to a solid floor?

Small boats generally are way more sensitive to load balance than larger ones - if you search the posts in the SIB section, there's lots of discussions about it. As a start, is your fuel at the front or the back (assuming it's a separate tank) - I guess you have a fair bit of fishing kit - where do you put it? A good rule is to shift weight forward - but do it slowly in case you go too far & enf up burying the bow when you're not planing.

Also if you don't have a solid bottom hull check your keel inflation - it doesn't take much of a pressure drop to make the keel totally useless which just means you get a ton of drag. If you donl' have a book of words that tells you the prssure it should be, post the make & model & I'm sure someone will have the numbers for you.

There is also the unfortunate law of nature that says to get on the plane needs a lot more power than it takes to keep you up there. You may find that when loaded, you have to move forward for a few seconds to help the hull over it's own bow wave. Once over that, you are skimming over rather than ploughing through the water, and you can move back again. A tiller extension will let you do that & stay in control.

Depending on your engines, it may be piossible to link them for steering with a bar, Having many years ago played with twin 2s (!) if one engine isn't enough to keep you on the plane, throttling back there is normally enough time to get the second one throttled back as the boat slows down. For manoevering, just use one engine & let the other tick over. For trolling you can switch one off & save fuel!

And welcome to the madhouse!
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Old 02 December 2009, 07:37   #8
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You got back befroe I finished typing!

Yeah, two 4- strokes is a lot of weight. 6Hp on a 3m should be a reasonable grunt, although you may need a lower pitched propellor. Someone like Locozodiac will be better placed to guestimate the correct size.
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Old 02 December 2009, 07:37   #9
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I think the extra weight on the back might cause a problem but it think there might be something else as i woiuld have thought 2 would be twice as fast.
Whilst you now have 12 HP you are presumably still spinning the same prop(s) - so if the engine achieves the same revs you won't go any faster. Twin engines are also less efficient than a single (more drag from 2 legs in water + dirty water gets thrown off one prop into the path of the other). In reality you would probably go faster with a 9.9HP as not only is it the inefficiency of 2 engines you have the weight penalty too - and that weight is right where you don't want it.

In reality 6HP is pretty marginal for getting a 3+m boat on the plane, especially if heavily loaded. To get on the plane you need to consider the following:

is the engine at the right height on the transom (typically antiventilation plate level with bottom of keel/transom).
is the engine trimmed correctly (angle of engine to transom). If bow is pointing at the sky - try trimming the engine closer to the transom (by moving the pin on the engine). [stupid factor check - make sure the engine is not in shallow drive mode]
is the weight distribution correct - to get on the plane you'll probably need weight at the bow. Get the fuel, anchor, gear and if possible yourself as far forward as possible.
is the prop right for the job. Changing prop might get you e.g. better acceleration to get over the hump.

then there may be options to consider like dolefins - but not till you've looked at all the above. of course trading in the two six's for a 9.9 would probably work better still!
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Old 02 December 2009, 07:49   #10
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might be best to post a couple of pics with your normal set up ,fuel tank / gear ect ,,with regards to your engines looking alike and being of the same badged power there could be a big difference in reality, suzi and johnson one could be rated at the power head the other at the prop depending on age,,though seeing now as they are both 4 strokes it wont be the case ,your problely wasting more fuel by having 2 engines running than just one for the extra few knots your going to get .with very small boats its sometimes better to have one engine fixed straight ahead non steer and then steer using the other engine .though you still have the throttles to contend with ,
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Old 02 December 2009, 07:58   #11
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atm,your so rude and twins on a dingy,come on please
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Old 02 December 2009, 11:27   #12
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I have checked my boat is a RIB it has a fiberglass v shaped hull and inflatable tubes. so not a sib i think.

My mate has a bigger propeller he is going to lend me, he is also trying to sell me a console I am worried this extra weight will make the problem worse not better.

Thanks for all your advice so far- theres more to this boating lark than i thought.

I will head down to the shed where she is stored and get a couple of pictures and post here. maybe tommorow if the rain stays off
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Old 02 December 2009, 11:43   #13
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I have checked my boat is a RIB it has a fiberglass v shaped hull and inflatable tubes. so not a sib i think.
that means she'll be relatively heavy so struggle more. generally speaking the deeper the v the harder to get it to plane also.

Quote:
My mate has a bigger propeller he is going to lend me,
bigger isn't always better - if you can't get over the 'hump' then I think you need more acceleration (smaller pitch prop) not bigger. If you get on the plane but not fast enough bigger might help, if you have enough power to turn it.
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he is also trying to sell me a console I am worried this extra weight will make the problem worse not better.
extra weight is not going to help - but it will be weight further forward which is a start.
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Old 02 December 2009, 15:54   #14
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So what kind of console are you thinking of putting on it. I presume it is a fairly small on as im guessing there wont be an awfull lot of room.
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Old 02 December 2009, 19:15   #15
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Sell your 2 6hp engines and buy one 15hp.
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Old 03 December 2009, 04:00   #16
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Sell your 2 6hp engines and buy one 15hp.
That's what i'd do,



Got a 2stroke Yammie on a 3.1m Avon and she has nnnoooo problems getting on the plane / airborne
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Old 03 December 2009, 04:18   #17
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If it's a solid floor then yes, it will be a touch heavvier, but I spent a summer at an outdoor centre with two 3m Avon solid floor things similar to what you have. 8Hp on the back of both and there was an interesting comparison - one had a Yam, the other had an older Mariner.

The mariner would get on the plane instantly, but the absolute top speed wasn't as fast as the yam, which needed a move forward (as mentioned before) to get over it's own bow wave, but once on the plane left the Mariner standing.

The Yam had a higher pitched prop.



As said, a console will add weight, but will shift the weight forward. A relatively cheap option might be to try a tiller extension, but that's not going to work safely with twins. When you get to the boat, have a look & see if there is a "max rating" on the transom.

I just pulled a manual from the Bombadier website- those 6 Hp 4- strokes weigh in at 30 odd Kg. to put that in perspective, the 4-Stroke 15 Hp weighs in at 44Kg. Save 20 Kg, gain 3 Hp & half your drag......

Having said that, it's probably worth playing with the propellors first. As a first check - when you're there taking photos, somewhere on the hub will be a number. Can you post them both- you may have two differnet props fighting each other as well.....
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Old 03 December 2009, 05:16   #18
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then there may be options to consider like dolefins
I was thinking the same, I have never had a set and I cannot comment on the performance change but, from the adverts they should make quite a difference.

Does anyone have experience of these?

Lee
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Old 03 December 2009, 05:37   #19
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Only thing with doelfins on this setup is that the engine is likely not bolted to the transom - will the clamps be enough to handle the extra lift? - Remember that they effectivley lift the back of the boat by the engine, and if it's loaded with fishing gear.....


I'd try (in this order)

- Move the kit forward, and try leaping forward at the right moment to get on the plane.
- Try a lower pitch prop
- Try a single bigger engine - (Even consider a 2-stroke which will be lighter).


The other thig that just crossed my mind - are they long or short shaft engines?
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Old 03 December 2009, 05:56   #20
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Doelfins make a bit of difference but not loads.
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