PLANING BOAT PECULIAR USE QUESTION

[Hot Property]

Reading this brought this boat to mine as we were moored near it during the summer.....
Sea Ray - Sedan Bridge 270 - FOR SALE - Harbour Yachts Poole

At 350 hours the engines aren't run in yet......

 

[jrudge]

This seems all pain and no gain.

You will put in an outboard, the control cables, a different instrument cluster. This will cost £££. Then you remove the old engine. Plug up the holes. This will cost £££. Then the c of g of the boat will be well out as it is not missing a large hunk of iron which it was designed around. Finally when you do what to get him early as the weather has turned, someone is ill etc you cant.

So you will have spent a load of money and a load of time. You are not bothered that the boats is also worth less.

Just go slowly. Simple.

 

[simonfraser]

have had similar thoughts myself and quite agree with your sentiments as long as you are not fussed over the money
But as you can 'just' swop to another v similar mobo with the OB already installed i'd def do that instead

and of course you can trial sail the OB boats and see what you are going to get

 

[Bouba]

To be honest, if it was me, I would look for a new boat and my only consideration would be my wife’s comfort. Easy for her to get on and off, move around and a comfortable secure sitting place so you can go fast if you want to. As a secondary consideration I would look for ease of use for single handed boating, that way you can go out with your wife and if she doesn’t have to lift a finger it could mean boating without pain for her and the option of going out by yourself. Just my two pence.

 

[kolyo]

The problem is that the hull speed of your boat is, in reality, more like 5-6 knots. The waterline length on these are only around 22ft. You will achieve hull speed with around 10hp. To go beyond, particularly into the realms of 10 knots will take a lot more power and use considerably more fuel. After 6 knots, the next most efficient speed is around 18 knots. 50-60hp won't, IMHO. be enough. Then there is the fact that a planing hulled boat is designed to plane. It will be pretty awful at displacement speeds in any sort of chop. I know you said you won't go out in chop, but in reality it is nearly always there to some extent.

The idea of around 18 knots max sounds interesting to me. What engine, outboard or inboard coupled to my present Bravo 2, will be able to achieve that with just me, my wife and not much stuff on board?

 

[kolyo]

Reading this brought this boat to mine as we were moored near it during the summer.....
Sea Ray - Sedan Bridge 270 - FOR SALE - Harbour Yachts Poole

Nice boat but too far from Greece .

 

[scottie]

The idea of around 18 knots max sounds interesting to me. What engine, outboard or inboard coupled to my present Bravo 2, will be able to achieve that with just me, my wife and not much stuff on board?

The one that’s already there with less foot on the gas

 

[Sticky Fingers]

The one that’s already there with less foot on the gas

Probably the best answer although if the OPs engine is falling to bits then maybe a case for re-engining. Don't know about OB conversion though? Seems a lot of work needed.

 

[skipmac]

First of all -- thanks for the input to all who took the time to reply, it's really appreciated!



1. No, my 454 is far from being high unto death with only 450 hours on the clock. But nevertheless'the engine is over 30 years old. Also it has several parts replaced with non-OEM ones by the previous owners, e.g. a cheaper Chinese exhaust manifold, starter, etc, On top of that there are some quite rusty areas, the most worrying of them being on the oil sump. Apart from that the over 3 decades old fuel tank is highly hazardous unless I don't replace it soon enough at quite a hefty price. Plus the rather unappealing cost of servicing an 8 cyl. inboard engine and a Bravo out-drive being about a grand p.a. Without making use of their full potential it seems a pretty extravagant expense to me.

2. I have fount too that a semi displacement speed is best for comfort in choppy condition. This is why I plan for a 50 or 60 hp high thrust outboard which (hopefully) will be able to push my not so heavily loaded 25-footer with a nearly 10 ft beam at about 9-10 knots.

3. Saving on fuel is the least of my worries. But the time wasted for frequent repairs or replacements is of HUGE concern. At my age every hour of boating I am allowed becomes equal to a week or even a month in the life of a much younger person.

1. Can relate. Currently have two power boats, an eight year old 22' with a 200 HP Yamaha outboard and a 26 year old 19' with a Mercruiser I/O. Have had to replace a few bits on the old Mercruiser and some bits are rusty (but not the oil pan as far as I can see) so do have some concerns about reliability. BUT, the newer boat with the Yamaha outboard I've been spending more on maintenance than the old Mercruiser. Main problem is constant cleaning of filters (there are four and the last requires significant disassembly to access) and injectors even though I winterize and add fuel stabilizer every year. It could be that I got a lemon model Yamaha but so far the Mercruiser which I would think would be the bigger problem has been the easiest.

2. 50-60 HP might be enough to raise the bow up a bit but, strictly guessing, I think it would be marginal. And you would still lose the option for planing and high speed if the need arose. What if you get a splinter in your finger and the local NHS clinic is closing in an hour and you're 15 miles away?

3. See comments on 1. above. A brand new outboard will probably reduce down time but at the end of the day, it's a boat. And you clearly know about boats.

 

[Hambleite]

If 18 knots is of interest, as you stated, then on your hull you will probably require enough power to plane, but then to be able to reduce power to an 18 knot cruise. Realistically this will require 150-200hp for your sized boat/weight if you're looking at an outboard.

So, say £12-17k for an outboard, £5-10k for hull modifications/installation....

I think I'd be looking at a re-power with a new petrol/diesel inboard and drive combination. This gives you the best all round result- new reliability, power if you need it, keeps the CofG relatively original, keep the boat you love.

 

[kolyo]

Would this be a viable option if I could find a D219 in good condition>

With a Bravo II 2,0 19" propeller and a bigger turbo.

 

[kolyo]

I think I'd be looking at a re-power with a new petrol/diesel inboard and drive combination. This gives you the best all round result- new reliability, power if you need it, keeps the CofG relatively original, keep the boat you love.

After a lot of deliberation I think I'll follow your advice.

Thanks once again.

 

[kolyo]

UPDATE. I received some additional advice from motor boaters with decades of experience and decided on the path I'm going to take. I'll keep the 7.4L Mercruiser/Bravo 2 leg for now and will do some tests next spring. What I will try to find out is if by using only a fifth of the 454's power (approx. 60 hp) I'll be able to control the boat in ANY wind or current condition I could ever encounter. If that proves to be possible I see no reason not to go ahead with the conversion by replacing the 30+ years old inboard gas guzzler with a brand new highly economical and environment friendly 60 hp Yamaha high thrust as my main engine.

 

[ontheplane]

Not sure I agree.

Seeing if your boat handles well with the 7.4 doesn't mean it will with the outboard because the boat will sit all wrong once you take out that huge V8.

We had a 21' with an 8hp and that reached 5kt so I don't think you need a 60 - probably a 30 or so would be better - although it may struggle in heavy winds - but you say you never boat in those.

I am actually with everone who says leave well alone and just don't use all the throttle - the v8 at tickover is producing more torque than a 60 would at half throttle - so see how much fuel it uses at tickover - and I suspect you're better keeping that engine and just replacing the iffy bits such as the oil pan and so on.

You say the tank needs replacing, but you'd have to do that with the outboard as well wouldn't you?? If not, would you use plastic tanks - if so you could do this with the v8 if you're running at tickover - it really won't use much fuel like that. You could increase the pitch of your prop as well if you don't need the ability to plane which might get you up to 5-6kts at tickover (if you aren't already doing that).

Also fit a rudder to the outdrive leg, at displacement speeds it will massively improve steering and straight line stability - again not good on the plane but that won't be an issue for you.

 

[kolyo]

Thanks for the input. I'm trying to find the best solution to my problems and what you said is really helpful. Did you mean this when you suggested adding a rudder?

 

[ontheplane]

Yup, anything like that.

My dad made a rudder for his old boat, simply bent 2 sheets of aluminium to right angle, bolted to cavitation plate. Doesn't need to be fancy. Will mean you can't really plane once you've done it as steering will become way too twitchy. Also helps reduce the paddlewheel effect on single engine. He tried a single rudder like in the picture and it helped a bit - but the two pieces of alu bolted either side worked way better.

 

[CLB]

UPDATE. I received some additional advice from motor boaters with decades of experience and decided on the path I'm going to take. I'll keep the 7.4L Mercruiser/Bravo 2 leg for now and will do some tests next spring. What I will try to find out is if by using only a fifth of the 454's power (approx. 60 hp) I'll be able to control the boat in ANY wind or current condition I could ever encounter. If that proves to be possible I see no reason not to go ahead with the conversion by replacing the 30+ years old inboard gas guzzler with a brand new highly economical and environment friendly 60 hp Yamaha high thrust as my main engine.

This chart seems to indicate that your 7.4 is producing about 60hp at idle (800rpm). If you try going everywhere at idle, that will give you an idea of what 60hp can do for you, but if you add a 60hp engine you will need to be at full throttle to produce 60hp, and that won't be much fun or very kind to the engine. Realistically, if you put a 60hp engine in the back, you will only really have 40-50hp to use unless you go everywhere flat out.

 

[kolyo]

...realistically, if you put a 60hp engine in the back, you will only really have 40-50hp to use unless you go everywhere flat out.

Now I get it. Looks like it would be way too much of a compromise if I replaced the 454 with a 60 hp outboard, be it a high thrust one.

 

[Alicatt]

My first dory ticked over at 6kt with a 85hp Johnson outboard on the back, just a bit fast for the harbour in Wick which had a 3knt speed limit, WOT on a good day was 37kt

 

[ontheplane]

Only other option is a 60-100 hp inboard diesel, doesn't have to be high-tech, in fact non turbo, nothing electronic might be better - you should be able to find something 2nd hand that could connect to the Sterndrive