Sadler 29 re engine

[Johnny WAFI]

Thanks to the many people who replied to my recent post. Very informative.

I understand the advice about sizing an engine to reach hull speed and in a calm sea the existing Bukh 20 is fine. But it struggles if I need to punch through a lumpy sea for example when leaving the Deben. I work the tides and you won't see me punching tide going up the Orwell with a huge bow wave! But an engine is also a piece of safety kit to get you home quick if something had gone wrong or to avoid a collision. Taking everything into consideration 20hp is fine but 24 or 25hp won't hurt. I agree that with 30hp I would be underloading the engine. By the way I don't have a rev guage but in calm neutral conditions the Bukh 20 feels happiest between 4 and 5 knots but not happy below 3 1/2 or above 6 knots.

 

[Tranona]

20hp is spot on for a Sadler 29. Hull speed is 6.4knots and you can just exceed that with the correct propeller. Poor progress in adverse conditions with your Bukh may well be because you have a 2 blade propeller and a 3 blade would be better.

As for replacement most engine ranges jump from 20 to 30 except Beta who have a 25. That will give you a potential for over 7 knots with cruising (5-5.5knots) at lower rpm. You will be able to swing a 1" larger diameter propeller which will reduce the loss in heavier conditions.

Which you choose will depend on how important motoring performance is to you and your budget. The 25 will add about £800 to your bill. However in terms of best performance under sail and motor allocating part of the budget to the propeller is important. It is the propeller that drives the boat, but it is also a big drag (literally) on sailing performance. The £800 difference is roughly the extra cost of a 2 blade folder like a FlexoFold which will not only give better motoring performance over a fixed 2 blade but improve sailing performance, particularly in light airs. So a 20 with a folder may be a better choice for the same money as a 25 with a fixed. Of course if there is no budget constraint a 25 with a folder will be a good choice also.

 

[neil_s]

I have a Bukh 20 in a Seal 28. 2 blade non-folding prop. Cruising at 5 and a bit knots is relaxing but I have no problem pushing the throttle right open for 6 1/2 knots when we get the big wash and the bow wave. Maybe your motor installation could do with some attention? If it feels uncomfortable over parts of the rev range, perhaps your mounts need replacement and the shaft needs alignment, too?

 

[doug748]

Beware of towing a huge prop and making a motor sailer out of a good sailing boat, 16hp would be fine 20 if you must.

 

[Tranona]

Beware of towing a huge prop and making a motor sailer out of a good sailing boat, 16hp would be fine 20 if you must.

Suggest you do the calculations as to what power and propeller is required for the boat. The original 20 hp was correct and a 20hp modern engine is a suitable replacement if required. Note that the OP is concerned about performance with his current engine in adverse conditions so perhaps suggesting he replaces the engine with one that is underpowered and will be worse than his current engine is not a good idea. He does not need a "huge" prop even if he went to a 25hp. The increase in diameter will be 1" and doubt he would notice any difference under sail. He would however notice a (positive) difference if he fitted a folding propeller as suggested.

 

[penfold]

I would posit that if it's still the original prop a modern replacement will yield a performance gain on its own, prop design and manufacturing have got better in 40 years, especially the folders. Physics won't let a sadler 29 go much past 6kts and 20hp is already more than enough to get there, more cowbell will just make noise and burn fuel.

 

[johnalison]

We used to cruise at about 5.7 kn in our Sadler 29 with 15hp and fixed 2-bladed prop. Since I tend to be shy of pushing engines, it may be that one could readily increase that slightly. My preference would be to go for a maximum of 20hp but consider a folding prop, which was not an option available to me at the time.

 

[Daydream believer]

Go for 25 HP & a folding prop. It is Ok doing 5-6 kts in flat water but one needs the punch in heavier seas. If you have that spare capacity then you can use it when you need it. You will not be doing 6kts in 1.5 M waves so max hull speed is irrelevant.

 

[doug748]

We used to cruise at about 5.7 kn in our Sadler 29 with 15hp and fixed 2-bladed prop. Since I tend to be shy of pushing engines, it may be that one could readily increase that slightly. My preference would be to go for a maximum of 20hp but consider a folding prop, which was not an option available to me at the time.

Just so.
The idea that you can tolerate driving a small boat of this type with the full power of an oversized engine is...
F F F Fanciful

.

 

[Kwik Decision]

I re-engined our previous Sadler 29 with a Beta 25 quite a few years ago now. Initially I was going to go for a 20; as others have said, that is more than enough to reach hull speed. But price and size difference in going to 25 was negligible (and the Beta 25 was still significantly smaller and lighter than the Bukh). This was coupled to a featherstream 3 blade feathering prop, and at full chat gave a little over 7 kts, with the stern sat right down such that the cockpit drains were under water. Normal cruising at 2000 - 2400 rpm gave around 5.5 kts depending on sea state. My conclusion, 20 is fine, but if you can still get a 25 for very little more money, then go for that. Also, factor in a new prop - the featherstream was brilliant, and made a significant difference when sailing in lighter winds, compared to the previous 3 blade fixed.

 

[Stemar]

Also, factor in a new prop - the featherstream was brilliant, and made a significant difference when sailing in lighter winds, compared to the previous 3 blade fixed.

There was an article in one of the yottie comics several years ago discussing the the merits of getting a gennaker or a spinny. The final conclusion was, neither. Get a folding/feathering prop instead, because that will give you much the same benefit, but on every point of sail.

 

[Johnny WAFI]

I would posit that if it's still the original prop a modern replacement will yield a performance gain on its own, prop design and manufacturing have got better in 40 years, especially the folders. Physics won't let a sadler 29 go much past 6kts and 20hp is already more than enough to get there, more cowbell will just make noise and burn fuel.

That is very informative. Thanks.

 

[penfold]

I have a Bukh 20 in a Seal 28. 2 blade non-folding prop. Cruising at 5 and a bit knots is relaxing but I have no problem pushing the throttle right open for 6 1/2 knots when we get the big wash and the bow wave. Maybe your motor installation could do with some attention? If it feels uncomfortable over parts of the rev range, perhaps your mounts need replacement and the shaft needs alignment, too?

Excellent suggestion, engine mounts do go off; they may still be intact and hold the engine where it's supposed to be but have changed characteristics and transmit more vibration to the hull. Slight misalignment can cause vibration too, which discourages use of the engine's full performance.

 

[Daydream believer]

Excellent suggestion, engine mounts do go off; they may still be intact and hold the engine where it's supposed to be but have changed characteristics and transmit more vibration to the hull. Slight misalignment can cause vibration too, which discourages use of the engine's full performance.

At a boat show I asked a mount manufacturer how long they should last & how I could tell when they needed to be replaced. Admittedly they were more interested in larger & commercial power units rather than my 20 HP Volvo but they could not give me an answer.
So how does one know?

A local outfit, fitted the 35HP Beta engine in my launch & put the wrong mounts in as well as miss aligned the shaft by 20mm. The vibration was really bad at under 1200RPM.
When I contacted Beta, they sold me the correct mounts & we re installed the engine. The difference was astounding. The engine now runs beautifully smooth.

 

[Tranona]

Just to add a few facts. The Sadler 29 has a waterline length of just under 23' and a displacement of 3.7tonnes (8500lbs). Its theoretical hull speed is 6.4 knots and the power required to achieve this is 18.5hp.

A 16hp is inadequate as it will not achieve hull speed but 6.19knots. 20hp will achieve 6.7 knots. Both of those need a 13" 2 blade propeller. A 25hp will achieve 7.19 knots with a 14" propeller.

Which to choose? Clearly not a 16hp if one wants the ability as the OP does to make headway in adverse conditions. The notion as suggested by some that smaller engine will lead to better sailing performance, or a larger engine will require a "huge" propeller and so affect sailing performance is simply not true. The 20hp is the obvious choice as the performance with the Bukh shows. The 25 has excess power and will need a 14" propeller, but has the advantage of allowing cruising at 2-300 lower rpm.

As already suggested the biggest improvement in both sailing and motoring performance comes from a better propeller. Either the Featherstream or FlexoFold will do the job. I have had both and my preference for this application would be the Flexofold which will give essentially the same performance as the Featherstreaam at lower cost. There are clearly advantages in the Featherstream to justify the higher cost, but they are of little benefit on a boat like the Sadler, unlike my GH where the extra blade area and ability to have a different pitch in forward and reverse are valuable.

 

[Scomber]

I re-engined our previous Sadler 29 with a Beta 25 quite a few years ago now. Initially I was going to go for a 20; as others have said, that is more than enough to reach hull speed. But price and size difference in going to 25 was negligible (and the Beta 25 was still significantly smaller and lighter than the Bukh). This was coupled to a featherstream 3 blade feathering prop, and at full chat gave a little over 7 kts, with the stern sat right down such that the cockpit drains were under water. Normal cruising at 2000 - 2400 rpm gave around 5.5 kts depending on sea state. My conclusion, 20 is fine, but if you can still get a 25 for very little more money, then go for that. Also, factor in a new prop - the featherstream was brilliant, and made a significant difference when sailing in lighter winds, compared to the previous 3 blade fixed.

14 yrs ago new beta 25 in our s29 too. Been v happy.