Maint Life 4.15 Years MSP 5,332 AFR 73% IFR 1.0% 1YR 495 5YR 7,424 Max Repair 1280 MSP
Right there, in black and white, is the reason the 20% MSP order "doesn't work" for you. Your max repair of 1280 is 24% of your total MSP. Therefore, your ship will not come back to resupply before it hits the possibility of bring unable to maintain itself. I recommend you add "sanity check max repair vs MSP" to your mental checklist when designing a ship.
For longer use survey ships I do, as mentioned the entire point of the design you pointed out was just to survey 2 systems away from a certain colony as it was growing significantly and had become a vital resource hub that I realised I hadn't explored around and wanted to know what's there, after it was done the entire design was retired and scrapped for reusing components/resources later (Which is why I was hesitant to initially paste it as I kinda expected the purpose would get overlooked for general design critique).
A example of my typical longer term ships would be the Voyager X class below the Horizon in the same post.
Maint Life 4.15 Years MSP 5,332 AFR 73% IFR 1.0% 1YR 495 5YR 7,424 Max Repair 1280 MSP
Right there, in black and white, is the reason the 20% MSP order "doesn't work" for you. Your max repair of 1280 is 24% of your total MSP. Therefore, your ship will not come back to resupply before it hits the possibility of bring unable to maintain itself. I recommend you add "sanity check max repair vs MSP" to your mental checklist when designing a ship.
I agree.. there is no reason to build a survey ship with engines that expensive, that makes zero sense to me. It has very strange deployment versus maintenance and general range capabilities.
You would need to put allot more engineering sections on this ship to make it a decent survey ship and it is way to expensive for that job in my opinion.
This is something a bit more streamlined for a survey period of about four years. You will never find a ship like that needing to ever get more supplies before the four years are up unless you are really unlucky.
Discovery class Exploration Ship 9,000 tons 221 Crew 1,048.8 BP TCS 180 TH 675 EM 0
3750 km/s JR 3-50 Armour 1-38 Shields 0-0 HTK 57 Sensors 33/33/4/0 DCR 13 PPV 0
Maint Life 7.55 Years MSP 990 AFR 48% IFR 0.7% 1YR 31 5YR 459 Max Repair 150 MSP
Commander Control Rating 1 BRG
Intended Deployment Time: 48 months Morale Check Required
J9000(3-50) Military Jump Drive Max Ship Size 9000 tons Distance 50k km Squadron Size 3
Naval Ion Drive 1500/60 (3) Power 675.0 Fuel Use 9.66% Signature 225.00 Explosion 6%
Fuel Capacity 504,000 Litres Range 104.3 billion km (322 days at full power)
EM Sensor Type-3 Mk-III (1) Sensitivity 33.00 Detect Sig Strength 1000: 45.4m km
Thermal Sensor Type-3 Mk-III (1) Sensitivity 33.00 Detect Sig Strength 1000: 45.4m km
Improved Gravitational Sensors (2) 4 Survey Points Per Hour
You also could skip on the jump drive to streamline them even more, but that require more manual work for the actual ordering of your survey efforts. You also could make bigger engines and go with two instead of three or even reduce the power multiplier somewhat to reduce the amount of fuel it require, but that is smaller stuff and it depends on what you have to work with.
That design you pasted is very much what I'd consider a early-game Sol and adjacent system only design. Speed, range and even tonnage size pretty much suited just for initial poking around Sol and not really practical for anything else. The reason for the larger engines in the prospect design was purely about speed and fuel efficiency for tonnage so it could quickly map out neighbouring systems.
With the Voyager X the engine size chosen is pretty much what I'd consider absolute minimum and comes down to fuel efficiency for the distances being covered whilst still providing what I'd consider a bare minimum speed to get anything meaningful done in its deployment time given the area it is going to need to cover. It won't just be poking around 1 or 2 systems from a refuel point, it's needing to cover multiple systems back and forth as I expand my map... to give some illustration:
Refuel options are Sol, Lankashiir and a orbitial fuel hub in Achillea (Though Achillea has since become a battle zone so not the best option). Whilst I could adapt something similar to your 9k design to make something larger that could cover distances realistically required, doing so and cutting down on max repair by requiring significantly smaller engines that consume much more fuel for lower output making the ship unfit for practical role purposes.
A surveyor that has a deployment time of 10 years but spends the half that time just moving systems giving the scope isn't really what I'd consider practical. So that leaves me with larger engines on the surveyors, though further messing around with the Voyager X concept has led to something a little more viable:
Voyager X class Survey Ship 16,000 tons 346 Crew 2,285.8 BP TCS 320 TH 2,000 EM 0
6250 km/s JR 3-50 Armour 1-56 Shields 0-0 HTK 101 Sensors 40/40/3/3 DCR 32 PPV 0
Maint Life 14.74 Years MSP 20,057 AFR 64% IFR 0.9% 1YR 173 5YR 2,592 Max Repair 800.0000 MSP
Captain Control Rating 1 BRG
Intended Deployment Time: 120 months Morale Check Required
J16200(3-50) Military Jump Drive Max Ship Size 16200 tons Distance 50k km Squadron Size 3
2000EP M-MCF 5k 0.072L (1) Power 2000.0 Fuel Use 7.24% Signature 2000.00 Explosion 8%
Fuel Capacity 3,257,000 Litres Range 506 billion km (937 days at full power)
TMS18 1k(50.3M) 113T (1) Sensitivity 40.50 Detect Sig Strength 1000: 50.3m km
EMS18 1k(50.3M) 113T (1) Sensitivity 40.50 Detect Sig Strength 1000: 50.3m km
Advanced Gravitational Sensors (1) 3 Survey Points Per Hour
Advanced Geological Sensors (1) 3 Survey Points Per Hour
This design is classed as a Military Vessel for maintenance purposes
Speed kept to similar levels but slight drop in ship range. EMS dropped to range similar to Thermal. Max repair cut down slightly and added just over 3 years to maint life along with doubling stored MSP with a trade off of 11% higher AFR which is a reasonably trade off in my mind.... just.
Pretty much what I'd consider to be a bare minimum survey design for the purposes intended but the significant jump in stored MSP should now mean the existing conditionals can finally serve their purpose long before the ship hits any kind of danger point.