A few questions. Drago Fiesta 600, Yamaha 50 o/b

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clb1970

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Hello everyone.
I'm new to the whole motorboating thing, only ever done anything with dinghys and small sailers before but have recently bought a Drago Fiesta 600 with a 50hp Yamaha o/b.

I took myself and 3 friends out for a potter last night and was disapointed to make no more than 15 knots, with the engine hitting about 4000 RPM with WOT. We checked the cabling and the engine seems to be getting max throttle. We didn't however check the revs with no load.

Could it be a) Too much load ? (although well within their limits) b) Wrong prop? c) Something else?

The engine has had a gentle life, is 5 years old with 100 hours on it and has been regularly serviced. The prop is in good condition. The boat is clean underneath.

Any suggestions or advice would be warmly welcomed.

Chris

(Sorry, forgot that not everyone will know the boat. She's a 20 foot/ 6.0 m GRP built forward cabin day cruiser type thing, planing hull and about 850kg wet displacement)
 
To be fair the 50HP was the minimum engine on that Package and meant more for Inland Waterways/Lake use. The most common package included a 75HP.

But do not panic, There are things you can do. Firstly you can either get the thrust to get you on the plane fast or a higher top speed by using a different prop. I would guess you have a smaller prop in it at the moment and may need a larger pitch if you want top speed but then you would be in real risk of strugling to get on the plane.

The first thing I would do is fit a 'Dole Fin' to the engine. This helps you get on to the plane and will keep you there at lower speeds. Once this is fitted you could then try a slightly higher pitch prop.

However the boat and engine package is just not going to be great. You may be able to push Top speed to nearer 17/18 Knots but that would be it.

One thing to check is that are you using New fuel or fuel already in the tank. If it is old petrol simply putting fresh stuff in will get an extra 1/2 knotts.

What engine are you using? Is it a Four stroke (Heavier) or two stroke? I have a 19ft centre console boat with a 90HP Evinrude two stroke on it. Total package weighs in at approx 850KG on the water excluding crew/ I get 32 knots from it as I have proped it down for lower planning.

The Drago is slightly heavier andv if you have a 4 stroke engine I bet the package is about 900KG so with only a 50HP you will always struggle a bit.

But remember, speed is not that imporatant. Most of us never open up our boats. I cruise at 19/21 knots and would only rarely do More. 15 knots will not set the world on fire but will get you comfortably from A-B!

Cheers

Paul /forums/images/graemlins/smile.gif
 
I have long suffered the same thing, and I'm afraid Nautorius is spot on, the whole rig is just underpowered for fast speeds. Take every single item off boat, no guests etc and you'll find it planes fine (albeit slowly).

There are options - the doelfin is one - and pitching the prop lower is another - both very cheap and definately the first thing to try.

Moving up the price scale, This is another option http://cgi.ebay.co.uk/Yamaha-90hp-outboa...%3A1%7C294%3A50

I have always been told the following which has worked well for me:-

Take the dry weight of the boat, add 100kg for each person you want to put on it and another 200kg for general kit.

for every 1000kg you then end up with as a total you need:-

up to 10hp per 1000kg for canals
20hp to 50hp per 1000kg for lakes, river light close coastal use but will struggle to plane
50hp to 100hp per 1000kg for estuarys of offshore coastal might plane with a struggle
100hp - 150hp per 1000kg for good planing performance, high speeds, skiing, ringos donughts etc
150hp + per 1000kg for a very fast boat.

That has always worked for me - but the key one in there is 100hp per tonne. If you have less than that (and on the boat we've used, 1800kg dry and 150hp) it is badly underpowered for planing, and the only thing we can do is re-engine, but with inboards that isn't practical, within a decent price bracket.

You are very lucky in having an outboard which by nature is easily changed, the one you have can be re-sold easily to offset the cost. If you keep your eyes peeled you might be able to find a decent priced larger outboard.
OR
http://cgi.ebay.co.uk/Yamaha-50hp-2-stro...%3A1%7C294%3A50 which is another Yam 50hp - I don't know the Drago, will it take a second outboard on the transom? If so, then this might be a very good idea, not only taking you up to 100hp (although speed wise 2 x 50hp will not be as fast as 1 x 100HP due to higher weight and extra drag)

If you want to go coastal at a decent speed, look for the CE plate, whatever the max engine listed is, you need to be within 20% of that otherwise you won't get the best out of the boat.
 
Hi Chris

Welcome to the forum.

You have had some good advice already but I have a question for you.
Regarding the top speed, up to now has the top speed been OK, is it down purely because of having your friends on board? What I am getting at is if you went out on your own, opened to WOT will you get max RPM? If not then you need to repitch/change your prop.
That will do for starters.
 
You could fit home-made permanently set ali trim tabs on the back which I did with mine. The problem is all the weight is aft, crew, engine, fuel and people. To get over the "hump" you really need to get the stern up, so moving everyone forward while you go max could get her up, they can then move back whilst she's up. Trim tabs, say 450 x 200 either side of the stern angled and fixed with rigging screws, (you'll have to play with the angle, around 7deg to start and adjust on trial with the rigging screws) will push the stern up for you.
 
You´ve had some good advice here and I would definitely second the suggestion of seeing how fast you can get the boat to go with just you on it. If you are not getting max RPM with full throttle, you can go to a smaller prop. If you are hitting max RPM you can go to a larger prop.

Just to give you an idea, my boat is a similar size to yours, but has 210HP. With a 21" prop on it, it hits 50mph with ease. But, with any more than 2 of us on board, it can struggle to get onto the plane (doing 10 or so MPH) and everyone has to move forward to help it go. With its original 19" prop, it hops up much more quickly, but then you don´t get the same top speed. So really some experimentation is needed to find out what works best for you.
 
Thank you all for the advice, just what I would have expected.
Unfortunately at the moment swapping engines isn't feasable (maybe next year) but I will try a no-load test and then a test with just me.

I'm not after absolute speed ( I wouldn't have bought the Drago if I was) but was more concerned with the engine not reaching full revs, which I beleive are 5-6,000 RPM (please correct me if I'm wrong). So if I can hit the upper rev range when more lightly loaded, I take it the prop is pitched incorrectly. Should I ask for further advice then?

Thanks again
Chris
 
Yep, try Your boat more lightly loaded.
Can You post the diameter and pitch of your prop?

Diameter is obviously the 'size' of the prop.
Pitch is the theoretically distance the prop will move the boat forward per one revolution.

IE a 12 inch pitch will move your boat 12 inches forward per one revolution.
So 'gearing' in effect is important.

I recently took a slightly smaller Drago than yours with a 90 hp for a Trip.
Albeit with 5 peeps aboard, a Large Dog and plenty of other stuff¬!

She worked ok
But She needed the horsepower to get on the plane.

Once 'up' She travelled along at 20kts at 3500 to 4000 revs no sweat.

You may need a more pitch to get up and away.
Then You can 'back off' the throttle.

Top speed may suffer.

But that's no sweat as long as you can get up on the plane.

With a bunch of peeps on board however, shunting them around will help enormously.

You mentioned flat out was 15 kts.
Which tells Me you are just about 'over the hump' ie just about to Plane nicely.
You aint far off Mate.
Oh! and welcome to this Forum.
There are some amazing bods on ere.

More peeps will give more info!
 
That's great.
I'm going to be away for the next week or so, then back for experimentation galore. I'll post prop diameter and pitch when I return. It's starting to make sense now, I think you're right in saying that its' too highly pitched and I need something lower to get the revs up.

Thanks again, Chris
 
Ok, the current prop is 11 5/8 diameter x 11 pitch and G series. Off to do some more testing with weight distribution and loading.
Chris
 
Just been out with less weight and played about with loading. A little better, but still won't pull more than 4300 RPM with WOT. No load, she'll rev happily above 6000 RPM and she's definitly planing, just not making full use of her rev range. Speed (according to the GPS, not the guage) is around 13 knots, which seems far too low. Again, I'm not worred about the speed, just being able to use all of her rev range.

So, off tomorrow to look at props and maybe a doel fin.

Any other ideas?

Chris
 
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