AD31p vs KAD32

[chillee]

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.

 

[BruceK]

Against tide she is struggling at times to keep up to planning speed

Your boat should not be aware of any tide other than from your observation speed over ground changes. If she is going into oncoming waves that is a different story. Before changing engine I'd make sure that mine is delivering optimal performance and correctly propped. I'm not sure what you should be reving at but it seems a bit low. A slightly finer pitch prop may be all you need.

 

[chillee]

Your boat should not be aware of any tide other than from your observation speed over ground changes. If she is going into oncoming waves that is a different story. Before changing engine I'd make sure that mine is delivering optimal performance and correctly propped. I'm not sure what you should be reving at but it seems a bit low. A slightly finer pitch prop may be all you need.

I never thought of it like that. Good point. Always seemed to notice the issue at it's worst around the same place after entering Southampton Water. So had assumed the tide ran stronger there as it was narrower

 

[Scubadoo]

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.

 

[Scubadoo]

I forgot to say, when fully loaded, drop your trim tabs down and make sure the outdrive is fully down, once on the plane raise the trim tabs, this does help a fully loaded boat.

 

[chillee]

I forgot to say, when fully loaded, drop your trim tabs down and make sure the outdrive is fully down, once on the plane raise the trim tabs, this does help a fully loaded boat.

Thanks. Yep, the trim tabs are a god send. One of them failed earlier last season and was sorely missed until I fixed it.
I was talking to Coataslrides in Dover earlier, and he believes an AD31p under load should not achieve more than 3900rpm.
I'm like you and can hit 4100 on a good day.
So he is also suggesting to consider reconfiguring my prop setup

 

[Scubadoo]

Thanks. Yep, the trim tabs are a god send. One of them failed earlier last season and was sorely missed until I fixed it.
I was talking to Coataslrides in Dover earlier, and he believes an AD31p under load should not achieve more than 3900rpm.
I'm like you and can hit 4100 on a good day.
So he is also suggesting to consider reconfiguring my prop setup

Heard this before about 3900rpm limit, it is simply not true as it depends on the AD31 variant, my Volvo manual states max 4100rpm for mine. Mind you I would never run my engine at max rpm, that is asking for trouble, I only do it as a test for a few minutes maybe couple times a year on my way back to home marina as a reference.

 

[QBhoy]

I might add an opinion.

I was very familiar with a friends lovely old cruisers 224 holiday with an ad31 150hp. She in fact was around 24/25ft in length and weighed in around or just over the 2 ton mark.
She would take a while to plane. Once you heard the engine come on boost, she would eventually get up with the help of the trim tabs. To keep her on plane you’d be at least 3/4 throttle usually. She would top out at about 25/26 mph trimmed up well.
I was fortunate enough to be able to compare this to the petrol AQ205 v6 GM 205hp version of the exact same boat. The difference was night and day in terms of performance, having the extra power on tap.

So fast forward a decade or so...the same friend now has a lovely and much more modern sealine S25 with a kad32 170hp. About the same size and I’d say a couple hundred kgs heavier even.
I was admittedly blown away at the performance she has for having apparently only 170hp. I’d be amazed if these kad32 are actually only 170hp. Not sure what others think...but I’d have a guess at saying they might actually be putting out much more than that. Around the 200hp region at a guess.
to compare the old cruisers with her ad31 and this sealine with itsKad32 is night and day. The low down grunt makes such a difference over the old ad31. Don’t get me wrong...putting the tabs down to help her plane is still the way to go...but once she is up and at it. This sealine was nudging on 36/37 mph gps from memory. Incredible I thought.

 

[madabouttheboat]

I might add an opinion.

I was very familiar with a friends lovely old cruisers 224 holiday with an ad31 150hp. She in fact was around 24/25ft in length and weighed in around or just over the 2 ton mark.
She would take a while to plane. Once you heard the engine come on boost, she would eventually get up with the help of the trim tabs. To keep her on plane you’d be at least 3/4 throttle usually. She would top out at about 25/26 mph trimmed up well.
I was fortunate enough to be able to compare this to the petrol AQ205 v6 GM 205hp version of the exact same boat. The difference was night and day in terms of performance, having the extra power on tap.

So fast forward a decade or so...the same friend now has a lovely and much more modern sealine S25 with a kad32 170hp. About the same size and I’d say a couple hundred kgs heavier even.
I was admittedly blown away at the performance she has for having apparently only 170hp. I’d be amazed if these kad32 are actually only 170hp. Not sure what others think...but I’d have a guess at saying they might actually be putting out much more than that. Around the 200hp region at a guess.
to compare the old cruisers with her ad31 and this sealine with itsKad32 is night and day. The low down grunt makes such a difference over the old ad31. Don’t get me wrong...putting the tabs down to help her plane is still the way to go...but once she is up and at it. This sealine was nudging on 36/37 mph gps from memory. Incredible I thought.

I would caveat that story with the fact that the 224 was never sold with 150hp AD31*, so the boat will have been messed around with at some point. It is possible it still had the old petrol leg and/or prop and wasn't operating at its peak.

I have owned boats with both AD31 and KAD32 and agree the KAD felt like it how more power than 170. In fact I have heard from a few sources that Volvo underrated it to avoid eating into the AD41 market that was still for sale when the KAD 32 was launched.

Sealine sold the S240 with AD31, that would be an interesting comparison to the KAD powered S25.

*ETA, the 224 was sold with the 130hp AD31 as a factory option. Just for info, it was also offered with the 167hp 4 cylinder AQ171 petrol and V6/V8 options up to 270hp. Top speed with the 167hp was 27 knots (31mph for QBhoy).

 

[kashurst]

As per BruceK - get your engine checked out with a very clean hull - could just be the turbo is past it's best and the injectors need freshening.
When the boat was new Volvo would not have signed it off if the performance was poor.

 

[QBhoy]

Was

I would caveat that story with the fact that the 224 was never sold with AD31, so the boat will have been messed around with at some point. It is possible it still had the old petrol leg and/or prop and wasn't operating at its peak.

I have owned boats with both AD31 and KAD32 and agree the KAD felt like it how more power than 170. In fact I have heard from a few sources that Volvo underrated it to avoid eating into the AD41 market that was still for sale when the KAD 32 was launched.

Sealine sold the S240 with AD31, that would be an interesting comparison to the KAD powered S25.

definitely original looking to me to be honest. Seen more than one for sale with that too. Had a 290/DPA or DPA (can’t remeber) with A series props.
Most are defo gm V6 for sure. But like the similar vintage sealine 218. Some must have had these fitted new...I presume.

 

[QBhoy]

I would caveat that story with the fact that the 224 was never sold with AD31, so the boat will have been messed around with at some point. It is possible it still had the old petrol leg and/or prop and wasn't operating at its peak.

I have owned boats with both AD31 and KAD32 and agree the KAD felt like it how more power than 170. In fact I have heard from a few sources that Volvo underrated it to avoid eating into the AD41 market that was still for sale when the KAD 32 was launched.

Sealine sold the S240 with AD31, that would be an interesting comparison to the KAD powered S25.

You may be right though. Not sure. I was convinced it was original, until you’ve put doubt in my head just now. Who knows.
just on the sealine 240 and ad31. I’ve been on one of those with this engine. Very very similar to what the 224 cruisers was, in terms of performance. Just didn’t suit the boat at all.

 

[chillee]

As per BruceK - get your engine checked out with a very clean hull - could just be the turbo is past it's best and the injectors need freshening.
When the boat was new Volvo would not have signed it off if the performance was poor.

Thanks for the suggestion. I did go through a thorough check over season before last, as had some serious performance issues. Ended up with new turbo. I'm also dry stacked now so nice clean bum. Mostly she is ok, runs lovely. It's just 4 largish adults seem to be testing her to the limits. Have read other reviews of ad31 boats and its often noted that with 2 up they are great . 4 can be a stretch.

 

[kashurst]

So down the boat today ,and the vinyl under the screen is covered in all sticky shit what is this and how do you stop it .

Thanks for the suggestion. I did go through a thorough check over season before last, as had some serious performance issues. Ended up with new turbo. I'm also dry stacked now so nice clean bum. Mostly she is ok, runs lovely. It's just 4 largish adults seem to be testing her to the limits. Have read other reviews of ad31 boats and its often noted that with 2 up they are great . 4 can be a stretch.

again as perBruce, try a slightly shallower pitch prop -might be enough to give that bit extra oomph onto the plane

 

[chillee]

again as perBruce, try a slightly shallower pitch prop -might be enough to give that bit extra oomph onto the plane

Yep agreed. I'm gonna be doing some prop research first i think, but like I mentioned, getting on the plane is not reay my biggest concern.

 

[madabouttheboat]

Was

definitely original looking to me to be honest. Seen more than one for sale with that too. Had a 290/DPA or DPA (can’t remeber) with A series props.
Most are defo gm V6 for sure. But like the similar vintage sealine 218. Some must have had these fitted new...I presume.

AD31P (the 150hp version) was launched in the mid 90's. The 224 was a late 80's boat. It also came with a DPD drive

 

[QBhoy]

AD31P (the 150hp version) was launched in the mid 90's. The 224 was a late 80's boat. It also came with a DPD drive

Ah. Ok. That makes a bit of sense. So it was likely the 130hp then. Suppose that would make a difference. The 224 was a 1989 year, from memory. Had the usual A series props on her, familiar to diesels like that.
The sealine 240 would be late 90’s I’d think.

 

[Scubadoo]

You may be right though. Not sure. I was convinced it was original, until you’ve put doubt in my head just now. Who knows.
just on the sealine 240 and ad31. I’ve been on one of those with this engine. Very very similar to what the 224 cruisers was, in terms of performance. Just didn’t suit the boat at all.

Should have said in my original post, mine is a S24 and disagree, the AD31:runs well in a S24 and found no issues with it getting on the plane as said earlier. The AD31 (150hp) was fitted to the s230, S240, S24 (same boat) from around 1994 to 2000, the very last year of production it was fitted with a KAD32 which then carried on into the S23 and s25, there were also petrol options too.

As the boat age, the engine is likely to loose a few hp and worth checking for example worn turbo.

 

[Scubadoo]

again as perBruce, try a slightly shallower pitch prop -might be enough to give that bit extra oomph onto the plane

Agree, I would be tempted to try J series (Eg. J5) duoprop which I heard some boaters had improve performance on acceleration, but lost a few knots top end which probably isn't an issue if you can improve the seawings 254 onto plane performance when loaded up.

 

[QBhoy]

Should have said in my original post, mine is a S24 and disagree, the AD31:runs well in a S24 and found no issues with it getting on the plane as said earlier. The AD31 (150hp) was fitted to the s230, S240, S24 (same boat) from around 1994 to 2000, the very last year of production it was fitted with a KAD32 which then carried on into the S23 and s25, there were also petrol options too.

As the boat age, the engine is likely to loose a few hp and worth checking for example worn turbo.

To be fair. When I mentioned the 240 with the ad31 I was on...it was far too easy to try to compare it to the other 3 240/24’s I’d also experienced. Two had 4.3 V6’s (one a Mercruiser and alpha one and one a VP 4.3 with DP) and one had a rarely fitted VP 5.7 V8 and DP. There was a really noticeable difference in power and ability between them all I suppose. I’m sure most of the time...the ad31 150 would do the job well enough though.