Review of Dehler 31
Basic specs.
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The hull is made of hand laid fibreglass. Generally, a hull made of hand laid fibreglass requires only a minimum of maintenance during the sailing season. And outside the sailing season, just bottom cleaning and perhaps anti-fouling painting once a year - a few hours of work, that's all.
The hull is a sandwich construction which improves the indoor climate. Especially when the water is colder than the air in the cabin, then the double hull insulates against cold water and reduce the condense water in the cabin. The core material in the sandwich construction is balsa.
The boat is equipped with 3 cabins and 6 berths.
The Dehler 31 is equipped with a fractional rig. A fractional rig has smaller headsails which make tacking easier, which is an advantage for cruisers and racers, of course. The downside is that having the wind from behind often requires a gennaker or a spinnaker for optimal speed.
The Dehler 31 has been built with different keel alternatives.
Deep keel
One option is a deep keel. A deep keel provide a better healing moment than a shallow keel.
The keel is made of iron. Many people prefer lead keel in favour of iron. The main argument is that lead is much heavier than iron and a lead keel can therefore be made smaller which again result in less wet surface, i.e. less drag. In fact iron is quite heavy, just 30% less heavy than lead, so the advantage of a lead keel is often overstated. As the surface of a fin type keel is just a fraction of the total wet surface, the difference between an iron keel and a lead keel can in reality be ignored for cruising yachts.
The boat can enter most marinas as the draft is just about 1.50 - 1.60 meter (4.92 - 5.22 ft) dependent on the load. See immersion rate below.
Fin keel
Another option is a fin keel. The fin keel is the most common keel and provides splendid manoeuvrability. The downside is that it has less directional stability than a long keel.
Dehler 31 can enter even shallow marinas as the draft is just about 1.45 - 1.55 meter (4.76 - 5.06 ft) dependent on the load. See immersion rate below.
The boat may be equipped with an inboard Yanmar diesel engine at 9 hp (6 kW). Calculated max speed is about 4.1 knots
Sailing characteristics
This section covers widely used rules of thumb to describe the sailing characteristics. Please note that even though the calculations are correct, the interpretation of the results might not be valid for extreme boats.
What is Capsize Screening Formula (CSF)?
The capsize screening value for Dehler 31 is 2.03, indicating that this boat would not be accepted to participate in ocean races.
What is Theoretical Maximum Hull Speed?
The theoretical maximal speed of a displacement boat of this length is 6.9 knots. The term "Theoretical Maximum Hull Speed" is widely used even though a boat can sail faster. The term shall be interpreted as above the theoretical speed a great additional power is necessary for a small gain in speed.
The immersion rate is defined as the weight required to sink the boat a certain level.
The immersion rate for Dehler 31 is about 165 kg/cm, alternatively 926 lbs/inch.
Meaning: if you load 165 kg cargo on the boat then it will sink 1 cm.
Alternatively, if you load 926 lbs cargo on the boat it will sink 1 inch.
Sailing statistics
This section is statistical comparison with similar boats of the same category. The basis of the following statistical computations is our unique database with more than 26,000 different boat types and 350,000 data points.
What is Motion Comfort Ratio (MCR)?
The Motion Comfort Ratio for Dehler 31 is 19.8.
What is L/B (Length Beam Ratio)?
The l/b ratio for Dehler 31 is 3.08.
The ballast ratio for Dehler 31 is 40%.
What is Displacement Length Ratio?
The DL-ratio for Dehler 31 is 183 which categorizes this boat among 'light racers'.
What is SA/D (Sail Area Displacement ratio)?
The SA/D for Dehler 31 with ISO 8666 reference sail is 17.4, with a 135% genua the SA/D is 20.0.
What is Relative Speed Performance?
The Relative Speed Performance for Dehler 31 is 69
Maintenance
As balsa wood is used as sandwich core material special care must be taken in relation to work that require penetration of the sandwich construction in order to to prevent water to get in contact with the balsa wood. Otherwise the balsa wood will eventually rotten and be expensive/impossible to repair.
When buying anti-fouling bottom paint, it's nice to know how much to buy.
The surface of the wet bottom is about 28m2 (301 ft2).
Based on this, your favourite maritime shop can tell you the quantity you need.
Note: If you use a paint roller you will need more paint than if you use a paintbrush.
Dimensions of sail for fractional rig.
Are your sails worn out? You might find your next sail here: Sails for Sale
If you need to renew parts of your running rig and is not quite sure of the dimensions, you may find the estimates computed below useful.
| Usage | Length | Diameter | ||
| Mainsail halyard | 29.3 m | (96.1 feet) | 10 mm | (3/8 inch) |
| Jib/genoa halyard | 29.3 m | (96.1 feet) | 10 mm | (3/8 inch) |
| Spinnaker halyard | 29.3 m | (96.1 feet) | 10 mm | (3/8 inch) |
| Jib sheet | 9.4 m | (30.8 feet) | 12 mm | (1/2 inch) |
| Genoa sheet | 9.4 m | (30.8 feet) | 12 mm | (1/2 inch) |
| Mainsheet | 23.5 m | (77.1 feet) | 12 mm | (1/2 inch) |
| Spinnaker sheet | 20.7 m | (67.8 feet) | 12 mm | (1/2 inch) |
| Cunningham | 4.0 m | (13.3 feet) | 10 mm | (3/8 inch) |
| Kickingstrap | 8.1 m | (26.6 feet) | 10 mm | (3/8 inch) |
| Clew-outhaul | 8.1 m | (26.6 feet) | 10 mm | (3/8 inch) |
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