AD31p vs KAD32

Yeh - I wonder if the answer is to change the boat if you are struggling.

Another option might be oversize trim tabs.

When I had an underpowered boat (Fairline Weekender with an AQ141 petrol) I looked up trim tabs, and then went for ones nearly twice the size recommended as I figured a longer (further back from the boat) and wider tab would exert more force on the water for a given angle of attack, or conversely would need less deflection for the same lift - I found them hugely useful, and they didn't need to be fully deployed to have a noticeable effect.

You may be able to use existing rams, and new tabs - or you may even be able to add length to the existing tabs? Might be a really cheap solution if it worked and easy to reinstate if it wasn't good.
 
Moodysailor said:
Just my tuppence worth here to add to it. I wouldn't suggest a 42 series engine for that as the extra weight in the back won't be offset by the increase in power. You will have to use a bucket load of tab just to keep it planing at lower speeds

The 32 is a completely different beast (as someone described it) to the 31 - it has so much more torque, and that torque comes in earlier. The only way you would get the benefit of the 32 though is if you changed the legs for the correct gear ratio too - then you would be able to use that torque. You can try it with prop sizes, but my best guess from memory (I used to manage a VP dealership) would be that you will be at the end of the prop size range and will be less than optimal.

I'm not personally convinced it's a viable upgrade, I just wanted to make the point that it's no just 20hp you are buying, and nor is it quite as simple as pulling out the 31 and dropping in a 32 then changing the props as that might not meet your expectation.
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Thanks for this good advice. And even if it was just changing the props, thats gonna be witch craft on such an unknown setup.
 
Partly Chillee but also you know what dia / pitch you currently have, so just drop an inch of pitch to get a bit more acceleration and cruise at the expense of a knot at the top end.
 
Scubadoo said:
I have a 25ft boat with a AD31, when I am fully loaded (fuel and water tank full) with either 4/5 people or in the past loads of dive gear, yes the boat will be slow to get up on the plane and I usually cruise at 19knots (most of the time) without any issues. When there is just 2 of us my boat feels quick to get up on the plane and cruise all day long. Your RPM 3500 is about right for 19/20knots, I set me speed by rpm, so I aim to cruise at 3500rpm depending on conditions and the speed is usually 19/20knots. Max speed is around 28knots (Max 4100rpm) which drops later in the season...boat will still plane but feel sluggish due to fouling, so top end I normally would lose about 200rpm (sometimes worse), this is improved when I get under the boat and clean the props and hull.

Your boat I think is slightly bigger and heavy than mine, so yes I think you boat will be slower (wouldn't say struggle though) when fully loaded, but really depends on a number of factors e.g. hull being clean, props clean, engine maintenance and so on.

The KAD32 will improve getting to plane and would be the choice between the two engines. But I'm not sure you will be greatly impressed with the difference, it is quite a cost outlay, so I would first consider changing the props or checking what you currently have set-up. Mine AD31 has A6 , but you could consider dropping to A5 or trying the J Series which I've heard can help getting on to the plane.
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chillee said:
Hi all, I know there has been some discussion on this, but I am looking for some real life comparisons please for a 25ft cruiser with ad31p(150hp) and same boat with KAD32(170hp)
I have a Hardy Seawings 254. Really like the boat, but she has an AD31p, and with 4 good size adults she really is right on the edge of coping. Against tide she is struggling at times to keep up to planning speed.
Fine with 3 adults, or 4 people where some are light weight.

I'm considering upgrading the engine to a KAD32.
I know the Supercharger will help me get up and out of the hole, which is nice, but not a major issue for me with trim tabs.
I'm just not convinced if the extra 20HP will give me that bit extra grunt at cruising speed, that will just make the difference to feel comfortable with 4 adults.

I'm currently cruising at approx 3500-3600 rpm to get 18-20kts cruising speed.
Interested to hear what your performance is like please on your 25fters.

Oh, and if anyone has a Seawings 254 or had one with a KAD32, super interested please to hear your views.
And on the off chance, did anyone fit a AD41 , KAD42 or KAD43 to their 25ft boat. I have space, but not sure what impact the weight will have.

Thanks.
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Hi, chillee

I have a 25 bayliner with ad31p 150hp
Just wondering how you got along this season and what the out come was with top speed and prop size I’m currently running A3 props and getting 17/18kts at 3700.

Thanks
 
Robert mcdonald said:
Hi, chillee

I have a 25 bayliner with ad31p 150hp
Just wondering how you got along this season and what the out come was with top speed and prop size I’m currently running A3 props and getting 17/18kts at 3700.

Thanks
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Having had and known a few bayliners around this size…I’d suggest the amount of fuel you have in them has a huge affect on how they go. Mine had a big fuel tank of about 200-250 litres just forward of the engine…so fairly well aft. When it was full…it really affected the performance. Even with the original powerful petrol engine (that yours likely had at one point). I’d think yours may be even more affected, given the much heavier diesel in yours now. Very stern heavy perhaps.
Leaving trim tabs down and trim down, would also lose you speed and rpm too. You might be able to find a few more mph and rpms yet.
 
I was out of action for a chunk of last season. trying to source a replacement power-steering pump reservoir.
I didn't go out with more than 3up, and she performed ok. Cruising at between 17 and 21 kts on GPS, depending on wind and tide. That at 3500-3600 rpm
She tops out at 4100 - so I am fairly sure the props a right. But I can't see any numbering on them, and don't have the tool to take them off.
 
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