Outboard Size

[Cladone]

Hi all, as I am honing in on a new boat and always had used boats and stern drives, the question of outboard has raised its head and a little confused. 

One particular boat im looking at is 6.5m length (waterline) 7m overall with dry weight about 1500kgs.

It used to be rated to Max 150hp but most recently updated that to 200hp.

If budget wasn't an issue I'd probably just throw a 200hp on the back, but that's not the case. 

Is there some way to determine what to put on the back if there was no way to test it?

I'm tossing up between Honda, merc and Yamaha and trying to get right power but minimise my expense. Or perhaps I should just wait till I can afford the 200hp, or perhaps a safe bet might be a 175.

Dont know a great deal about this technical stuff

[rickmarlin62]

what type of hull  flat underneath ?  Lifting strakes  beam width  deep v  planing hull ?? Lots of variables  more info would be handy   2st or 4st

[noelm]

What sort of 7m hull is rated to a max of 150hp?

[noelm]

Depending on the HP might influence your motor choice, they are all good motors, but some better than others for a certain HP.

[zmk1962]

1 hour ago, noelm said:

What sort of 7m hull is rated to a max of 150hp?

I suspect it's something like a Jeaneau ... @MerryFisher has one at around the 6m mark thats rated for a 115hp.  He does well with that. I saw one 7m Jeanneau demo at the 2017 boat show with a 150HP Merc on the back.

Having said that and based on my experience, choosing an outboard is less to do with the single HP rating that has been assigned to a motor and more to do with what torque output that motor produces between idle and 5252rpm. 

As per my recent experience repowering my boat from a 200HP 2str to a 150HP 4str resulting in better performance and fuel economy up to 70km/h....if I do the HP calcs on my 150HP Merc, I can derive a rating of 177HP for that motor from the torque / rpm curve. But marketing chose to sell it as a 150HP motor ... you can conclude why !

In my post below, I have mentioned several other European manufacturers using this 150HP motor on their 1500kg dry weight rigs.

Hope this helps.

Cheers Zoran

[campr]

Its risky exceeding the recomend max hp for a hull.  If manufacturer has reccently increased max hp I would check with them that they haven't beefed up the hull or transom before accepting that this relates to your boat.  Just a thought?   Ron 

[zmk1962]

5 minutes ago, campr said:

Its risky exceeding the recomend max hp for a hull.  If manufacturer has reccently increased max hp I would check with them that they haven't beefed up the hull or transom before accepting that this relates to your boat.  Just a thought?   Ron 

....and that's why marketing choses a HP rating for the motor vs the true MAX capability of the motor .... so they get max applicability to hull manufacturers.

.. the motor manufacturers stay within their justification that the motor can be rated as a 150HP and the hull manufacturers are comfy it   meets the hull load rating.

Cheers Zoran

Edited October 1, 2020 by zmk1962

[Cladone]

Hi guys sorry I didn't receive notification of replies. It's a parker pilothouse 660 much like the merry fisher correct. Really nice boat and great ride. Used to be 150max now 200hp. Many are running around on 115. I have an option of a 150 Honda, or 150 merc or verado 150 with only 20hrs on it. 

[Cladone]

Anybody with any experience at all with a 150hp verado? 

[Cladone]

Yes good point, making sure to what boats the Max hp applies and why the change... 

[Cladone]

Sorry of course I can reject all options and for some added coin get merc v6 175 or whatever 

[Cladone]

On 10/1/2020 at 7:48 PM, zmk1962 said:

I suspect it's something like a Jeaneau ... @MerryFisher has one at around the 6m mark thats rated for a 115hp.  He does well with that. I saw one 7m Jeanneau demo at the 2017 boat show with a 150HP Merc on the back.

Having said that and based on my experience, choosing an outboard is less to do with the single HP rating that has been assigned to a motor and more to do with what torque output that motor produces between idle and 5252rpm. 

As per my recent experience repowering my boat from a 200HP 2str to a 150HP 4str resulting in better performance and fuel economy up to 70km/h....if I do the HP calcs on my 150HP Merc, I can derive a rating of 177HP for that motor from the torque / rpm curve. But marketing chose to sell it as a 150HP motor ... you can conclude why !

In my post below, I have mentioned several other European manufacturers using this 150HP motor on their 1500kg dry weight rigs.

Hope this helps.

Cheers Zoran

This is very interesting. The 150 merc seems a good fit. What's the deal with SOHC 8 valve and others with DOHC 16 valve etc. What part does that play? 

[wrxhoon1]

150 Merc is a simple engine with one camshaft and 2 valves per cylinder, has been around a few years now and proven to be reliable . Others are more modern engines with 2 cams and 4 valves per cylinder.

It depends on what you want on a boat as to the HP. If it was me I would opt for a 200 HP V6 merc, same weight as the 175 and not much heavier than the 3.0 lt 150 Merc. You will pay a bit more but you are never going to be sorry you got max HP . If you got the 150 you may, then again it may suit your application.

I don't know about the 150 but the 200 you can get it with DTS. 

I don't know who owns Parker now or where they are made but for a big (heavy?) boat the max rated HP is fairly low .

[Cladone]

1 hour ago, wrxhoon1 said:

150 Merc is a simple engine with one camshaft and 2 valves per cylinder, has been around a few years now and proven to be reliable . Others are more modern engines with 2 cams and 4 valves per cylinder.

It depends on what you want on a boat as to the HP. If it was me I would opt for a 200 HP V6 merc, same weight as the 175 and not much heavier than the 3.0 lt 150 Merc. You will pay a bit more but you are never going to be sorry you got max HP . If you got the 150 you may, then again it may suit your application.

I don't know about the 150 but the 200 you can get it with DTS. 

I don't know who owns Parker now or where they are made but for a big (heavy?) boat the max rated HP is fairly low .

Parker is made in Poland. Yes I am surprised also and even more surprised that until recently it was rated to 150hp. I have seen a number of videos of this boat which also goes by Aleskadden P66 or something like that in Norway with 115s on it and it going quite well. I'll hopefully be taking one out in the next week. It is very much in the spirit of the arvors and merry fishers. Ticks a lot of boxes for some good fishing but family cross over and competitively priced. 

 

Ultimately I'm not a speed freak over extended distances. Like many the main considerations is moving between positions quickly when fishing, or needing to get out of curious situations etc... Don't want it to be sluggish, a good quick and nimble and responsive movement is main concern... Top end speed not so much. 

 

But for example I can probably get just for example a 150 Honda for 19k installed at the two helms, a Honda 175 with drive by wire for about 23k installed, yet a yammie 175 or merc v6 about 28k fully installed, so not merely a marginal difference and if not needed then...

[zmk1962]

Based on my experience you will need to add about 1K or more to those prices for installation and any additional gauges that you may want. 

BTW, don't think that "simpler" means old and inefficient and "modern" means better. Motor's are designed for specific applications and consumer markets.

I chose the 150 Merc ProXS because of weight, cost, reliability, and ease of access to a reputable marine mechanic. The 150 was the lightest in the 150 class, and from my research it punched well above that and into the 170 range- especially on the torque it produced across the full rev range from its 4cyl 3L powerhead.

It had some 30% less moving parts (SOHC design) than its competitors - so it was designed ground up to be simpler to maintain, and service and be less costly to do so - from the powerhead to the oversized lower leg gear box. Less parts = less things to go wrong. There is a life time warranty on the SOHC valve train and a 6yr overall warranty. It was built to be a workhorse.

So that tells you the designers thinking behind SOHC.  The base 150 has been around for a while and the ProXS version came out in 2018. It added a bunch of technology like Transient spark, that increased WOT to 6000 and reduced fuel consumption while increasing torque about 5-8%. The 150 does not come with DTS.

Twin cams can drive more valves and hence by allowing the cylinders to breathe more (increase volumetric capacity) - they can derive more power for those that need it at the cost of more moving parts and complexity. Merc moved to a 6Cyl 3.6L block with DOHC as the basis for 175+ engines ... think there is a 8cyl range now as well.

Anyway... there's a lot to digest in all of this. Probably easier to talk. Send me a PM and we can organise a time to chat if you want.

Cheers Zoran

[noelm]

There's a lot to be considered when buying a new engine, don't let a brand sway your decision, I have said this before and got flamed for it, certain brands are better than the others in certain HP ranges, some are heavy, some are simple, some are expensive, some have little support network, so you need to take what you want from your motor, then research, don't simply rely on internet hype about brands, you will have to sift through pages of rubbish to gather information.

[Cladone]

31 minutes ago, noelm said:

There's a lot to be considered when buying a new engine, don't let a brand sway your decision, I have said this before and got flamed for it, certain brands are better than the others in certain HP ranges, some are heavy, some are simple, some are expensive, some have little support network, so you need to take what you want from your motor, then research, don't simply rely on internet hype about brands, you will have to sift through pages of rubbish to gather information.

Yes I have done this. Quite frankly I don't care about brand as such. Whichever engine gives the type of performance I'm looking for and represents good value, but has at least a strong foundation for general reliability then that's all I need. 

To that end, I note Honda is usually an undisputed king in reliability, yet I also see academically at least it probably not best performer compared to some of these others. 

Everybody always says dealer network, but I've always understood and experienced that if your local mechanics know how to work on a given engine whether Honda, Yamaha or merc and use genuine parts etc that's what matters isn't it with warranty and the like?

Take Honda, there are not many dealers in my area, but plenty who know how to work on them and so long as genuine parts used etc warranty unaffected. So I never understood this sentiment, although my experience with outboards is limited and maybe I'm plain wrong about the point. 

 

 

[zmk1962]

Sure, the basic principles are the same. Simplicity of service was a key consideration for me, that's why I stayed away from super charged / blown engines, and for basic items (change of oil, plugs etc) a 4 stroke is a 4 stroke.

However, most of the new engines have ECU / computer controlled engine management. A generic mechanic is unlikely to have invested in the engine diagnostic system and the training for different makes and brands ... at my 20hrs service the mechanic had printed off what looked like a >15page report from the engine management system - log of events, errors, readings - he was able to pinpoint the date and time of a burst of WOT in reverse and questioned that (happened to be when I was reversing boat off stuck trailer rollers at low tide). It was a non event, but the event could have been an overheat, or gradual increase in temp over a given RPM range ... small indicators that something was staring to fail. Out of spec events are flagged early giving you time to address them before a failure.

I have chosen to have my engine management data linked so that it transmits to the cloud  - and I have given my mech access to it. 

Reliability is important to me with the offshore boating I do ... so this adds to my peace of mind. 

Cheers Zoran

Edited October 3, 2020 by zmk1962

[zmk1962]

One additional thought just came to me. 

@Cladone it sounds like you are buying a package (probably new), it would be interesting to see what propeller specifications they are recommending for the different brands of motors - not all 150HP are the same - and the motor manufacturer will have more say on the prop specifications than the boat dealer.  

The size and pitch of prop that a particular motor can spin - will have a major effect on the overall boat speed, efficiency and performance (lively or slug).

So as an example if a motor manufacturer  is recommending a 13in pitch for that 7m 1500kg application, to give the boat good hole shot, it means that motor is developing the required torque at high rpm... high rpm at that early stage means you have high fuel consumption already and you have very little top end left before you hit WOT... so lively and nimble at hole shot but at the cost of top speed and fuel overall.

Cheers Zoran

[Cladone]

Just adding some additional investigations to determine some experienced thoughts from this forum. 

I've been assisted by a member on this forum very generously and I'm grateful. The information obtained has clarified many aspects I was confused about. 

Since that discussion it occurred to me that this 1500kg dry weight pilothouse is quite bow heavy. I noticed it on weekend when took it for a run. If all weight in pilothouse or forward from amidships you could tell it would dip slightly at bow. 

In speaking with a friend who is pretty knowledgeable and to the point, his thought process which made sense logically was that...

The boat is rated to 200hp.

Neither the specific boat design (nor my intended use) is really designed for racecar performance.

With load all geared up and any engine choice looking at maybe 2.5t on the water overall. It's a heavy-is boat. 

He recommended something like the new Honda 175hp v6 with drive by wire. It's gear ratio is 2 to 1, it will produce good low and mid range torque and will be fuel efficient and enable you to reach cruising speed and also accelerate very quickly. The gear ratio is also suitable to boat type. 

Added to that it is a heavy engine maybe 70kg more than mercury 150. That will add some balance to the bow heavy situation too. 

Does anybody disagree with this reasoning and why? 

My initial thought was that it all made sense. Then questions started creeping in such as is adding a much heavier engine the answer, would its weight nullify the added power, or will it be able to push boat with ease not overworking and be more fuel efficient.... Just after some further thoughts on the issue to crystallise these relatively confusing concepts in my mind generally

[zmk1962]

Balancing load in any hull will improve performance.  2.5T is heavy.... 1000kg above 1500kg dry weight... 

When you tested it, what load was in the boat?  How much fuel, water, how many people?  Where were the people standing? 

A 200HP does negate all the thinking ... after all its the max the boat can take. 

I am not as familiar with the Honda as I am with Merc. 

The Merc 175 and 200hp have the same weight 216kg, so 10kg heavier than the 150hp... are you sure the Honda is 70kg heavier??

Both the Merc 175 and 200hp have option of DTS - digital throttle and steer (drive by wire)

Cheers Zoran

[Cladone]

5 minutes ago, zmk1962 said:

Balancing load in any hull will improve performance.  2.5T is heavy.... 1000kg above 1500kg dry weight... 

When you tested it, what load was in the boat?  How much fuel, water, how many people?  Where were the people standing? 

A 200HP does negate all the thinking ... after all its the max the boat can take. 

I am not as familiar with the Honda as I am with Merc. 

The Merc 175 and 200hp have the same weight 216kg, so 10kg heavier than the 150hp... are you sure the Honda is 70kg heavier??

Both the Merc 175 and 200hp have option of DTS - digital throttle and steer (drive by wire)

Cheers Zoran

Honda is also digital throttle drive by wire. I think the suggestion for Honda came for combination of weight and gear ratio to move the boat nicely and easily relative to the mercs. 

Yeah Honda is like 280kg or something if I recall. 

In terms of boat when tested three were on board, maybe 250kg between us, he had heaps of fishing and camera equipment and gear, 100l in tank, engine another 200kg or thereabouts so it was probably up there. I'm just being conservative allowing 2.5t once loaded with anchor and chain, fishing gear, refrigeration, 5 to 6 people, engine fuel and water... It wouldn't be that far off 

[Cladone]

4 minutes ago, Cladone said:

Honda is also digital throttle drive by wire. I think the suggestion for Honda came for combination of weight and gear ratio to move the boat nicely and easily relative to the mercs. 

Yeah Honda is like 280kg or something if I recall. 

In terms of boat when tested three were on board, maybe 250kg between us, he had heaps of fishing and camera equipment and gear, 100l in tank, engine another 200kg or thereabouts so it was probably up there. I'm just being conservative allowing 2.5t once loaded with anchor and chain, fishing gear, refrigeration, 5 to 6 people, engine fuel and water... It wouldn't be that far off 

And no doubt 200 would negate it but would be overkill for the boat, plus balancing budget, fuel efficiency and just wanting the right weight and most suitable engine that's all. Whether it's 150 through to 200 not fussed as such just trying to work out most suitable whatever it may be. 

The boat with the weight I stated above had the 150 merc 4 stroke and seemed to be fine. We discussed the proxs and I was sold it would be sweet, then started hearing need heavier engine to compensate for bow heaviness, v6 would be more fuel efficient and work less hard to achieve cruise etc so just started having more questions 

[zmk1962]

Let me try and disect what you are saying ... hopefully it will help.

1 hour ago, Cladone said:

The boat with the weight I stated above had the 150 merc 4 stroke and seemed to be fine.

I'm sure as tested the boat already had an anchor/chain as that is a requirement to be on the water.

So out of curiosity was the boat bow heavy when tested? If it was and it ran fine with the 150 that means the designer took that bow heaviness at rest into consideration and built in the strakes and bow shape to generate bow lift when underway.

BTW, to get to your max load where would the extra weight be placed? It seems you want to accomodate extra 3people over the test case - can an additional 3 fit in the bow area - or would they be midship to stern?, ... also if the tank was topped up to full with the extra 40L of fuel ( the tank is usually mid to stern underfloor) if so this weight would be to the back anyway. 

1 hour ago, Cladone said:

then started hearing need heavier engine to compensate for bow heaviness

I would not put on a heavier engine if there is a lighter equivalent HP engine just to compensate bow weight. You can always trim your motor out a bit when taking off to lift the bow and then tuck it back in when under way.

1 hour ago, Cladone said:

v6 would be more fuel efficient and work less hard to achieve cruise etc

Not sure there is a test for how "hard" a motor has to work... "hard" is a subjective term not often used in mechanics...  but since it all comes down to spinning the prop, which requires the motor to spin,  I guess a good measure is at what RPM does the motor generate the torque/HP to get the job done.

Fuel efficiency ... well it depends. It comes down to volumetric capacity (fuel air mixture) to deliver the motor's torque/horsepower. Speaking Merc specs again.

4cyl 3.0L capacity = 750cc per cyl. 

6cyl 3.4L capacity = 567cc per cyl 

Four-stroke & 4 cylinders engine => 0.5 * 4 = 2 sparks per revolution

Four-stroke & 6 cylinders engine => 0.5 * 6 = 3 sparks per revolution. 

The 4 cyl has significantly fewer moving parts to work.

So again it comes down to at what RPM do these motors generate their torque/HP ... to spin the prop.

If the prop RPM was identical, then for each RPM the 6cyl would use more fuel, and has more moving parts working (harder??)...so the 6 would have to be able to push you along at lower engine RPM to be more fuel efficient and to work less hard is my way of thinking.

On the 150HP you tested spinning the 15p prop, with a 2:1 lower leg gear ... this is what you shared with me: 

20kts (23.0mph) engine 3500rpm, means prop at 1750rpm (max theoretical speed of 15p 24.8mph) pretty close

32kts (36.8mph) 5400rpm(?), means prop at 2700rpm (max theoretical speed of 15p 38.35mph) pretty close

Not sure at what RPM the boat hit planing speed and how long it took to get there (holeshot)... but the above stats look pretty good. 

Maybe if someone has 6cyl  they can share at what RPM they hit these speeds (plus the weight of their rig and the prop dimensions).

Cheers Zoran

[zmk1962]

Sorry .. Maria called pen's down for dinner ... so to finish the thought process above ...

I'd want to see a commitment that the v6 Merc can spin an 18p prop and deliver the above performance before I'd concede equivalence on fuel consumption and hard work... (that should equate to about 10% drop in engine RPM for same boat speeds. 

Thats just my view... other more engine knowledgable folks can chime in with their experience.

Cheers Zoran